Search Documents

By K. Regl, J. Berneder

"AMAG investigated different aspects to improve the resistance against grain coarsening in aerospace alloys during recrystallization and was successful in finding several opportunities to minimize this effect. The studies show that one aspect to counteract grain coarsening is the chemical composition and subsequently all phases that are formed during homogenization. Starting with a fine grain (~ 50 µm) can lead to a final grain size of few mm. On the other hand with a coarse initial grain size (approximately 150 µm) and the right chemical composition the grain size can stay almost constant despite different deformation steps. Additional we investigated different sequences for the component production to eliminate the problem of grain coarsening as a coarse grain has a detrimental effect on product performance.INTRODUCTION In the aircraft industry, aluminium sheets are most commonly deformed in their soft state, followed by solution heat treatment and natural or artificial aging. If the preceding deformation is in a critical amount, during the recrystallization at solution heat treatment grain coarsening can occur. A subsequent deformation to this condition leads to an orange peel surface, which requires additional polishing. Next to this extra effort the coarse grain size produces a drop in the mechanical properties, often below specification limits. If there is no subsequent deformation, this effect is not visible and without destructive testing there is no possibility to detect the error. As mentioned before, this effect occurs during recrystallization, which is a process that is driven by the stored energy in the microstructure. The two most important aspects for an increase of the stored energy are the increase of the grain boundaries fraction (smaller grain size) and the increase of the dislocation density caused by deformation. The increase in dislocation density during the deformation arise from trapping of existing dislocations and from the generation of new dislocations. During recrystallization all grains are built completely new, so all dislocations are removed (Humphreys & Hatherly, 2004). There are three requirements for recrystallization:"

Jan 1, 2018

By R. Salimi

Tricalcium aluminate hexahydrate (TCA) is used as filter-aid for security filtration in the Bayer alumina process. TCA is typically produced on-site by mixing Bayer liquor with slaked lime. Specific properties are required from the TCA to ensure adequate filter throughput, lifetime and importantly effective reduction of solid/colloidal impurities from the solution. The effect of reaction time on morphology and particle size distribution of tricalcium aluminate was studied for a batch experiment at simulated process conditions. It was found that reaction time plays a critical role on the morphology, crystal structure (diameter and crystallinity) and particle size distribution. In the early stages of the reaction, nucleation dominates the crystallization process followed by growth dominated by agglomeration up to a mean particle size of 10 µm. The particle morphology shifted from an irregular shape to more spherical throughout the course of the reaction.

Jan 1, 2014

By Madaah Hosseini H. R., P. Abachi, S. Miraghaei

In this study, the effects of milling time, chemical composition and heat treatment on microstructure and magnetic properties of nanocrystalline Fe-Si (6.5-25 at.% Si) alloys prepared by mechanical alloying have been investigated. The results show that increasing the milling time or the Si content, decreases the lattice parameter and increases the internal microstrain. The prepared powders mainly consist of micron-sized particles with an average grain size of less than 20 nm. The specific saturation magnetization values are slightly less than those of single crystal or conventional Fe-Si alloys and decrease as Si content increases. The coercive force values of the nanocrystalline as-milled powders are much higher than those of corresponding Fe-Si bulk alloys with a minimum at 13.5 at.% Si. The values of coercive force decreased after annealing but it seams that the residual strain developed during milling is not the major contributing factor to the higher values of coercive force in the mechanically alloyed powders and nanocrystals behave as single-domain particles without exchange interaction between them.

Jan 1, 2006

By M. Rylatt, E. Legault-Seguin, C. Mohns

"With energy costs increasing and ore grades diminishing, the role of preconcentration in hard-rock mining operations has gained greater interest. Dense medium separation is a process that can be conducted at particle sizes from 250 to 0.50 mm with high separation efficiency, depending on liberation characteristics of the valuable minerals. Pilot-plant case studies conducted at the SGS Lakefield site are presented, including mineral systems such as spodumene, sulfide-bearing gold ores, and complex sulfide ores. These case studies demonstrate that, for amenable ores, mass rejection of 20–60% is possible while maintaining recoveries of greater than 90%.RÉSUMÉ Au vu de la hausse des coûts liés à l’énergie et du déclin de la teneur des minerais, le rôle de la préconcentration dans les exploitations minières en roche dure présente un intérêt croissant. La séparation (ou concentration) en milieu dense est un processus pouvant être mené sur des calibres de grains de 250 à 0.50 mm avec un rendement élevé de séparation, en fonction des caractéristiques de libération des constituants des minéraux métallifères. Sont présentées dans cet article des études de cas menées dans des usines pilotes du site de Lakefield de SGS, lesquelles incluent des systèmes de minéraux tels que le spodumène, les minerais aurifères sulfurés et les minerais sulfurés complexes. Ces études de cas montrent que pour les minerais présentant les caractéristiques de libération appropriées, il est possible d’atteindre un rejet en masse de 20 à 60 %, tout en maintenant des récupérations supérieures à 90 %.INTRODUCTIONPreconcentration is the process of rejecting gangue minerals while ensuring recovery of valuable minerals prior to more intensive, downstream processing. Preconcentration has been practiced in the industry for many years, and is gaining greater interest as the industry copes with processing lower grade, more difficult ores, which typically require finer grind sizes and incur higher energy costs.The benefits of preconcentration are:• lower mining costs, which allows for nonselective mining;• lower process capital and operating costs (e.g., resulting from reduced grinding, flotation, and fines disposal stages);• increased ore reserves, which provides the potential to treat lower grade ore;• increased mine production without expansion of the existing plant or concentrator;• reduced overall tailings impoundment by converting the reject into a byproduct (e.g., underground backfill or aggregate);• improved efficiency of downstream processes (e.g., silica removal in electric arc furnace feed, removal of softer sliming minerals prior to grinding);• potential application to brownfield operations and greenfield projects; and• a “green” process option, which reduces processing energy consumption;– reduces mill feed;– increases stage metal recovery (higher grade feed);– increases mill metal output per tonne processed;– reduces surface plant, tailings dump, and tailings pond requirements because the plant has a small footprint and can be installed underground; and– can be applied to retreatment of old tailings dumps to recover metal values and reduce environmental impacts (e.g., dissolved metal runoff, acid drainage)."

Jan 1, 2017

By J. Koike

Mg alloys for structural application have attracted much attention. However, high process cost and poor mechanical reliability are major concerns upon expanding the application to a wider area. In order to break through these barriers, better ductility is desired at lower temperature. Plastic anisotropy and peculiar twin formation appear to play key roles in the deformation and fracture mechanisms of Mg alloys. In the paper, dislocation slip and twin formation are reviewed. The effects of crystallographic texture and grain size are discussed. The results suggest that a good control of microstructure and texture can improve ductility and mechanical reliability of Mg alloys.

Jan 1, 2006

By Yan Germain, Université Laval, Bernard Dallaire, Jocelyn Bouchard, Peter Radziszewski, Gilles LeBlanc, Michelle Levesque, Nicolas Tremblay

"The comminution process is estimated to be only 1% efficient, resulting in waste energy dissipated as heat, noise, and vibration. Energy recovery from grinding circuits has not been implemented mainly because recovering heat from the surface of the grinding mill or from mill slurry can impede operation, increase maintenance requirements, and prolong plant shutdown time (and production). However, currently very little information is available in the public domain regarding the amount of waste energy and that potentially recoverable in the grinding circuit of a mineral processing plant. Availability of such information could drive innovation and improve decision-making regarding opportunities for waste energy recovery. The Canadian Mining Innovation Council (CMIC) has initiated a study with CanmetMINING and mining industry partners to develop a model to map the energy flows in grinding circuits and to quantify the potential for energy recovery. The paper outlines the underlying fundamentals and data requirements for use in the model and then focuses on quantifying the energy recovery potential of the semi-autogenous grinding and ball mill circuits at the Agnico Eagle Goldex Division. Results show that most of the electrical energy (over 75%) is used to heat the slurry, leaving only a relatively small amount of it to achieve mechanical work (~9%). INTRODUCTIONCanmetMINING commissioned a study in 2013 to better understand the barriers for adoption of new technologies in the mining industry (MNP, 2013). The conclusions highlighted the importance of enhancing industry/regulator engagement and communication to raise awareness and improve the industry’s comfort level with new technologies.In November 2014, the Green Mining Innovation Advisory Committee (GMIAC) held a workshop to explore the possibility of accelerating the uptake of green mining technologies by bringing together key stakeholders among the mining value chain to address industry priorities. Participants included representatives from mining companies and associations, academia, provincial governments and federal departments and organizations. Two key priority areas emerged at the workshop: i) energy saving, and ii) water management."

Jan 1, 2016

By S. R. Amos, N. O. Lotter, A. L. Hannaford, J. F. Oliveira, D. W. Broughton

"Ivanplats Ltd appointed Xstrata Process Support to perform the flowsheeting development work for their hypogene and supergene geomet units of the Kamoa Copper deposit, located in the Democratic Republic of the Congo. Through systematic flowsheet development using modern Process Mineralogy, the optimised milestone flowsheet delivered a saleable concentrate grade of 32.8% Cu at 85.4% recovery with hypogene ore, and a saleable concentrate grade of 45.1% Cu at a recovery of 83.4% for supergene ore. The significant value of this development is that a single flowsheet will treat both hypogene and supergene ores and produce saleable concentrates. Further work to advance the flowsheet performance has been identified for investigation in the near future.INTRODUCTIONLocation and Description of the Kamoa DepositThe Kamoa copper resource is located some 40 km west of the city of Kolwezi, in the south west of the Katanga Province of the Democratic Republic of the Congo, in the region of Central Africa. Drilling at Kamoa in 2008-2009 had discovered laterally continuous, sediment-hosted, high-grade stratiform copper mineralisation in a newly discovered copper district that forms a previously unrecognised western extension of the famous Central African Copperbelt – which hosts such world-class deposits as Kolwezi, Tenke-Fungurume, Konkola and Nchanga. This discovery showed that the western end of the Copperbelt in the Congo does not terminate at Kolwezi (Friedland & Broughton, 2009). The resource contains hypogene and supergene geomet units with a transitional zone located inbetween the (upper) supergene and the (lower) hypogene. In the hypogene unit, the major copper sulphides are bornite, chalcopyrite and chalcocite, whilst in the supergene, the sequence is led by chalcocite, then bornite, and finally chalcopyrite. Covellite is present in both units as a minor copper sulphide. Both geomet units will be mined and treated in one concentrator, either as blends or as campaigns."

Jan 1, 2013

By A. L. Nunes, J. R. E. Garcia, G. Silva, U. Prasad, C. Rabe

"Drilling through the Guayabal shales, a gray calcareous shale, and the C1 to C100 formations, a well-cemented calcareous-sandstone in Corralillo field, Mexico, is a challenge due to severe wellbore instability problems. Additionally, there has been a history of ineffective reservoir stimulations by hydraulic fracturing. To predict and mitigate these subsurface issues, it is essential to characterize the mechanical properties and rocks strength for a better prediction of borehole stresses and collapse pressure during drilling. Various correlations can be used to estimate and/or determine the unconfined compressive strength but most of them are based on transit time and porosity.In this study, grain size distribution was combined with acoustic travel time, porosity and static Young’s modulus to develop a rock strength prediction model for the turbiditic sandstones of the Chicontepec basin. The main reason this combination of parameters was employed was because of the wide variations in rock strength estimated using traditional porosity-based correlations such as the McNally’s (1987), GMI-Jizba-E’s and Bradford’s (Bradford et al., 1987).To develop a new correlation, a geomechanical and microstructural campaign was initiated. Mineralogy by X-ray diffraction, pore and grain sizes by petrography, clay distribution by SEM and porosity by mercury intrusion porosimetry were measured. Static and dynamic Young’s moduli and Poisson’s ratios were acquired by triaxial and ultrasonic measurements on undisturbed sandstone samples from the Chicontepec basin. More than ten offset wells with wireline data, including transit time, porosity, density, resistivity and gamma ray, were used for reservoir and geomechanical characterizations.Our analyses lead us to propose a new correlation for predicting the uniaxial compressive strength (UCS) of sandstones of the Chicontepec Basin as a function of transit time and grain diameter, both of which can be derived independently from destructive laboratory tests. Our results also highlight the importance and value adding of a combined approach incorporating grain size analysis in the rock strength prediction. The UCS predicted using the transit-time and grain-size-based model presents a median value (P50) of 76 MPa, P10 of 55 MPa and P90 of 89 MPa."

Jan 1, 2015

By Ram Song, Yohei Harada, Shinji Kumai, Kazuho Otsuka

"Recently, vertical-type high-speed twin-roll casting (HSTRC) has been developed. The HSTRC shows extremely high cooling rates over 1,000 K/s even at the mid-thickness area. The fabricated strip has many metallurgical characteristics; super-saturation of alloying elements, fine solidified structure, and homogeneous distribution of fine constituent particles. In Al-Mn based alloys, the Mn alloying element can be supersaturated in the a-Al matrix and also form Mn-containing constituent particles during solidification. The Mn supersaturation and the distribution of primary/secondary particles in cast products affect the metallurgical behavior in the down-stream processing and can improve mechanical properties of the final products. In this study, Al-Mn based alloy strips were fabricated by HSTRC with various Mn contents. The solidified microstructure, constituent particles and its distribution, and Mn solubility were investigated in the as-cast condition. Due to the high cooling rate of HSTRC, fine constituent particles were homogeneously distributed, and coarse intermetallics were not observed. Mn solid solubility was estimated by electrical conductivity. The estimated Mn solubility was equivalent between strip surface and mid-thickness area.INTRODUCTION Al-Mn based alloys, as non-heat treatable wrought aluminum alloys, are widely used in packaging and heat exchanger for automobile industry. Besides Mn, Al-Mn based alloys often contain Fe and/or Si as alloying elements or natural impurities. During solidification, Mn can be super-saturated in the Al matrix, and also form Mn-containing constituent particles. Additionally, in the subsequent thermal-mechanical processes such as homogenization, rolling, and intermediate annealing, Mn in solid solution precipitates out of the Al matrix as secondary particles. The size, distribution, type, and the amount of dispersoids including constituent particles affect to texture evolution, recrystallization behavior, and final mechanical properties of wrought Al-Mn based alloys (Huang et al., 2016; Huang & Marthinsen, 2015; Engler et al., 1995; Muggerud et al., 2013). Therefore, controlling the initial level of Mn super-saturation and the distribution of constituent particles are important in the cast Al-Mn based alloys."

Jan 1, 2018

By Y. Yhang, D. C. Sego

ABSTRACT This paper evaluates the potential of freeze-thaw dewatering using Albian mature fine tailings (MFT). Freezing tests were first performed to study the effect of freezing rate on dewatering efficiency. Lower freezing rate resulted in higher thawed solids content and shear strength. Subsequently, large strain consolidation tests were conducted to investigate consolidation behaviour and how it is affected by freeze-thaw. The consolidation behaviour was presented in terms of effective stress versus void ratio and permeability versus void ratio. The results can be used to predict the field behaviour of Albian MFT and optimize the application of freeze-thaw for MFT dewatering.

Jan 1, 2014

By D. Runnels, Daniel Roy, Ricardo Esteban, J. Torrealba-Vargas

"An intuitive way to reduce power consumption in grinding operations is to feed the grinding circuit with finer feed by enhancing blasting and fragmentation control. The optimization of blasting with the objective of minimizing power consumption in grinding is not new.The study was based on a Canadian mine that processes a very hard ore. BBA conducted blasting/fragmentation and grinding circuit surveys in 2014. The results of the exercise were used to develop a base case model to simulate the effect of blasting in the operation on the grinding circuit. Tools for fragmentation simulations, particle size measurement and crushing/grinding simulations were used with the objective of reducing the OPEX costs including power consumption.The paper describes the steps involved in the model optimization as well as an economical evaluation of the OPEX savings.INTRODUCTIONIn 2014 BBA was retained by one of its clients to conduct a crushing and grinding survey. The objective of the survey was to update the grinding circuit model with production data and also to develop a tool to investigate opportunities for process improvement.A second phase of the study involved the development of drilling and blasting and crushing models. The models were used to diagnose the operations and to investigate opportunities for process improvement.The objective of the present study is to describe the approach and to identify potential improvements to overall mine site operating costs by better integrating mining and milling operating costs with blasting and grinding models."

Jan 1, 2016

By L. Bratek, K. Jaworek, M. Czaplicka

Methods for arsenic compound removal from aqueous solutions include processes such as: coagulation, adsorption, membrane techniques, electrochemical and biotechnology techniques. Advanced oxidation using both UV radiation and strong oxidizing agents such as ozone and hydrogen peroxide may also decompose these compounds. It is known that effluents from metallurgical processes contain inorganic arsenic compounds in addition to the organic compounds such as: dimethylarsinic acid and phenylarsonic acid. This paper presents the conditions that lead to the formation of deposits containing mainly arsenic, such as pH, the wavelength of the radiation and the type of oxidant, for this type of effluent.

Jan 1, 2014

By A. A. el-Geassy, A. A. el-Tawil, Hesham M. Ahmed, Bo Bjorkman

The Iron and steel industry is one of the most intensive energy consuming processes. The majority of iron making processes is now directed towards the uses of fossil-based energy sources like coke, coal and oil. Recently, emphasis has been paid to replace part of fossil- based energy sources with renewable biomass-derived reducing agents. In the present work, the possibility of the effective use of woody biomass in carbon-iron oxide composites was investigated. Wood powder was carbonized in N2 atmosphere at 300 up to 450oC. The carbon content in the produced bio-char increased with temperature. The porosity of the char arises from maintaining the cellular structure inherent in wood biomass increases with temperature. The reduction behavior of four iron oxide-bio char composites having different fixed carbon content were carried out non-isothermally up to 1200oC in Ar atmosphere using thermogravimetric anlyser (TGA). Quadruple mass spectroscopy (QMS) was also adopted to measure the CO, CO2 concentrations in the off gases resulted during reduction process. The effect of volatile matter on the reduction of iron oxide was intensively studied. The different phases developed in the reduced product were identified by X-ray diffraction (XRD). The reduction of composites was found to proceed in a stepwise manner (Fe2O3?Fe3O4?FexO?Fe).

Jan 1, 2015

By S. Kashani-Nejad

The kinetics of the thermal decomposition of samples of Mg2(OH)3Cl.2H2O that were obtained by a novel leaching technique applied to a commercial magnesium electrolysis feed were investigated under ambient atmosphere. Thermogravimetric (TG) Analysis showed that decomposition of Mg2(OH)3Cl.2H2O exhibited a single intermediate stage wherein crystalline water was lost at roughly 108 °C. Conversion of the resulting Mg2(OH)3Cl to MgO, HCl and 1120 occurred at temperatures above 398 °C. Thermal decomposition of anhydrous Mg2(OH)3Cl was seen to be consist of two stages. Both stages exhibit first order kinetics with respect to the weight percent of Mg2(OH)3Cl remaining in the sample. However, the rates of decomposition in the two stages were significantly different. Detailed analysis of the kinetic data suggested that the rate of decomposition of Mg2(OH)3C1 was controlled by the rate of removal of the gases released. The change in decomposition rate during the course of the experiments was explained by HCI being released in stage 1 and followed by release of H2O in stage 2.

Jan 1, 2004

By Henry Stoch

It?s a green, green world ? Public concern about the impact of human activities on the environment and the roles that businesses play in that impact is rising. What?s happened in the last few months? ? Recent news: ? British Columbia announces carbon tax in 2008 budget ? Federal Court ruling stalls oil sands approvals due to a lack of consideration of GHG implications ? US Energy Independence and Security Act could limit government procurement of oil sands-derived fuels ? Western Climate Initiative (WCI) suggests a ?first seller? approach for regulating generators outside WCI jurisdictions ? Implications ? A cost for carbon has arrived ? The lack of a GHG strategy can have a material impact on your business ? Regulations in other jurisdictions could affect your organization

May 1, 2008

By A. V. Corlett

MR. C. S. Gibson: Mr. Chairman, I listened with much interest to Mr. Corlett's paper. Those of us who are directly engaged in mine ventilation and dust control are impressed by the improved atmospheric conditions to be derived from the use of methods of mining such as those in operation at Aldermac, which Mr. Corlett has just described, and those employed at Noranda. It is a well known fact that drilling-dust is one of the most potent factors in the production of silicosis in mines handling ores containing quartz, so that from that angle the use of diamond drills, instead of percussion drills, to drill ore for blasts in stopes is an important development. A second point which I think merits mention is blasting. Blasting, we all know, creates the most dust in a mine and the fact that you can drill ore for a large blast with diamond drills and fire it, say, on Saturday night, and then have all the next day to ventilate the workings, is a great advance in dust control. 1 have wondered if Mr. Corlett, or possibly those at Noranda, can en-vision the use of the diamond drill as a means of advancing cross-cuts and drifts, preparing stopes, etc. I believe it is a matter which is receiving considerable attention at the moment in some parts of the world and J thought it would be interesting to have Mr. Corlett's reaction on that point. MR. A. V. CORLETT: I am not quite so hopeful of using diamond drills as a means of drilling holes in the ordinary drift. Maybe some of the diamond drill men can give us some further information on that point. MR. R. D. LoNGYEAR: The diamond drill manufacturers are working on that problem, but until further work is done we have nothing definite to offer. Drilling holes with a diamond drill to compete with rock drills for advancing drifts and cross-cuts is a desirable objective, because of the elimination of drilling dust and the ability to cut a smooth bore of uniform diameter. To reach this objective, higher rates of penetration are required, which can only be achieved by discovering the optimum bit rotating speed, by reducing vibration, and by further improving the bits and machines. We are optimistic, but the problem is still largely in the research stage.

Jan 1, 1940

By T. C. Murphy, W. Taciuk

In 1966, the Iron Ore Company of Canada commissioned a wet magnetic scavanging plant for the recovery of fine magnetite values p.resent in spiral tailings discharged from a spiral gravity separation process. The plant includes dewatering, grinding, classification, thickening, mini-wedge screening, and primary, secondary and tertiary wet magnetic separation stages. The source of feed varies in quantity and quality, so the original design included variable operational procedures to deal with these conditions.

Jan 1, 1972

By V. Aprahamian, G. B. Harris, C. W. White, M. Tangen

"In 2005, the Royal Canadian Mint (RCM) commissioned a new silver electrorefining circuit. This circuit was intended to operate with a minimal electrolyte bleed for the control of copper. However, by the time of start-up, the levels of copper-rich silver doré to electrorefining had increased, and despite partial pyro-conversion in a small Top Blown Rotary Converter (TBRC), copper concentration in the silver anode still averaged 7.5%. This necessitated frequent replenishment of the electrolyte with fresh silver nitrate since copper displaced dissolved silver during electrolysis, and therefore requiring a robust copper bleed treatment step in order to maintain cathode silver flake purity at 99.99%. The originally-installed bleed treatment system could not meet the RCM’s needs. A thorough review of known technologies, however, did not indicate one capable of handling the copper load, and resulted, therefore, in the development of a novel copper hydrolysis approach for removal of copper as an insoluble basic nitrate salt, and recovery of the associated nitric acid for re-use in the circuit. Laboratory-scale trials showed reproducible results, and existing equipment was subsequently modified.INTRODUCTIONIn 2005, the introduction of a new silver electrorefining circuit at the Royal Canadian Mint (RCM) initiated changes in the way customer silver, collected from the gold doré circuit, was processed. These circuit changes were discussed in a recent paper (Aprahamian, 2015). A wastewater treatment plant had not been budgeted at the time, and this represented a significant constraint when considering the introduction of a wet processing circuit. After a review of various options, a turnkey silver electrorefining circuit was purchased from a European firm. Initially, enough cells were ordered to produce 2 million oz of fine silver (999), with the option to increase to 5 million oz. The selected equipment was based on a Moebius cell design combined with a silver grain pressure dissolver to produce make-up silver nitrate solution. Additionally, an evaporator/hydrolysis unit included in the package appealed to the Mint Refinery, on the basis that it offered a simple way to bleed dissolved copper in electrolyte without generating effluent."

Jan 1, 2016

By A. L. Irwin

THE problem of compensation for labour is probably the oldest and most complicated one in history. The wage that a man receives is possibly the most concrete thing he gets out of his job and, rightly or wrongly, is generally considered by him to be the most important item in connection with his daily work. How today workers in an equitable way has been the study of industrialists for many years, and a great number of ideas have been tried out in an effort to arrive at a reasonable solution of the question. The idea of establishing a measuring stick for various types of work has intrigued industrial management for a long time and, after considerable study, the principle of Job Evaluation has taken form unti1, at the present time, it is becoming increasingly useful to industry at large. Job evaluation is a plan which is used to determine the relative worth of occupations by means of arbitrary measuring scales. These scales are developed for individual industries and are generally 'tailor made' for each particular case. There are as yet no absolute methods of measuring the work done by human beings and, as a result, one has to depend on comparative values to arrive at conclusions. However, job evaluation has provided us with a basis of negotiation for wage rates which is more satisfactory than mere guess work or persona! opinion. It supplies a common ground for discussion which is understandable by all taking part and ensures that thinking with regard to wage setting is carried out along standard lines.

Jan 1, 1943

By B. J. McKay, K. Schneider, H. B. Nadendla

"A series of experiments were conducted to assess the impact of zinc additions on the morphology and soundness of the interface of Al-Mg compound castings. It was found that high amounts of zinc (>15wt%) are necessary to affect the morphology and microstructure of the interface. At these zinc concentration levels, the formation of the zinc-rich phases t1 and ? were observed along with the Al-Mg intermetallic phases ß and ?. The micro hardness of all phases across the interface was found to be similar, ~200 Hv. This even hardness gradient is thought to avoid mechanical failure in the interface under load. In samples containing large concentrations of zinc (>15wt%), the formation of bubble shaped voids as well as the complete transformation of the aluminium alloy was observed. While the exact mechanism causing the voids has not been identified it thought to be connected to the Kirkendall effect. INTRODUCTION Conventional single material components are increasingly failing to meet the demands, in terms of cost and performance, of the transport industry. Compound castings have been identified as a promising alternative as they possess a number of benefits (Bührig-Polaczek, Röth, Baumeister, Nowack, & Sussmann, 2006). Compound casting is described as a process in which a metallic melt is cast around a solid metal shape. Preliminary research has concluded that for the stability of such a resultant hybrid structure it is imperative that both metals form a sound connection via form closure, force closure, or material bonding. A continuous material bond between the two metals is also highly desirable as the formation of a crevice between the metals could lead to galvanic corrosion, particular in a humid environment (Lao, 2013; Rübner, Günzl, Körner, & Singer, 2011). Even though Al-Mg compound castings could offer the biggest potential in terms of weight savings to date only a limited amount of research concerning such structures exists."

Jan 1, 2018