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Influence of variations in alloy composition on castability and process stability. Part 1: Gravity and pressure casting processes

Abstract The influence of variations in alloy composition on the fluidity of three different light metal alloys was investigated. The aluminium alloys AlSi9Cu3 (A380) and AlSi7Mg (A356) as well as the magnesium alloy AZ91 were cast into spiral fluidity test dies at their upper and lower compositional tolerance limits. The test results show significantly varied behaviour, which is explained by microstructural features and heat content. In alloy AlSi7Mg at the upper compositional limit the formation of intermetallic phases in the interdendritic liquid physically blocks the flow and leads to short flow length compared with the same alloy with low iron and manganese content. Alloy AlSi9Cu3 at the upper compositional limit is very close to eutectic composition and flows significantly better than the alloy at the lower tolerance limit. The intermetallic phases are formed simultaneously with the matrix during eutectic solidification and do not block the flow. In the magnesium alloy the intermetallic phase is incorporated in the primary magnesium phase and does not hinder the flow. A higher content of alloying elements increases the flow length owing to a higher heat content of the melt.