Metallurgical and foundry parameters for the SSM forming of high strength aluminium-zinc-magnesium-copper (7075) alloy

Aluminium-Zinc-Magnesium-Copper, 7075, alloy offers both high strength (comparable with those of alloy steels) and very good ductility which makes this alloy group suitable for many automotive, aerospace and defence applications, however the alloys are difficult to cast because of their tendency for Hot Tearing. The Semi-Solid Metalforming (SSM) casting technique allows for near net shape casting using High-Pressure Diecasting (HPDC). The lower forming temperature reduces the problem of Hot Tearing. The CSIR has developed a rheocasting process which prepares semisolid slurries from molten metal which can then be formed using HPDC. Since 7075 is a wrought alloy there is limited information on the foundry practice for this alloy. The aim of this study is to determine the foundry practice for 7075 aluminium alloy. Melting trials and optical emission spectroscopy on, AA7075 was conducted to study the effect of metallurgical melting parameters and compositional variations. 7075 Alloy was melted using a resistance melting furnace and compositional variation in the crucible for varying holding times was evaluated to determine the degree of segregation of key alloying elements. Results have shown some compositional variations.