Metallurgical Properties of Large Aluminium Alsi7mg03 (A356) Sand Castings

A 500kg aluminium AlSi7Mg03 casting has been poured and the metallurgical quality at different locations inside the casting has been thoroughly investigated. It included measuring the local tensile properties (YS, UTS, El) in the T6 condition, the dendrite fineness (DAS) and the level of microporosity. A correlation was found between the microporosity level, the local solidification time and solidus front velocity; this correlation allows to predict the porosity level in large aluminium castings (solidification times between 20 and 200 minutes). Quite expectedly, properties varied widely within the casting and the actual mechanical properties were much less than the "textbook values" based on measurements carried out on separately cast standard specimens. A correlation between the secondary dendrite arm spacing (DAS) and the local solidification time was in keeping with previously published data. Finally the conditions to obtain an acceptable finish on machined surface were determined.