The effect of temperature on soldering and the sequence of formation of the soldered layer during high pressure die casting of Al-11Si-3Cu alloy

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Abstract
Soldering is an important cause of die failure in high pressure die casting (HPDC), but mechanisms of the formation of the soldered layer are not clear. In this study, HPDC soldering experiments with Al-11Si-3Cu alloy have been conducted using core pins as soldering targets. Due to heat loss in the process, soldering reactions in the die cavity occurred at temperatures equal to or below the liquidus temperature of the cast alloy. Local solidification time was found to be the determining factor for the severity of soldering. Hence, in thicker sections of the casting, the pin was in contact with the solidifying alloy longer than in thinner sections and therefore required less cycles to solder. Soldering started with the formation of intermetallic outbursts accompanied by build-up of solidified cast alloy. A soldered layer developed by the growth of soldering intermetallics via a solid state reaction, together with coarsening of the phases in the cast alloy layer adjacent to the soldering intermetallics. The fracture path separating the casting and the soldered pins during casting ejection was usually in the cast alloy rather than inside the intermetallic layers. This may be related to the poor bond strength between the existing soldered layer and the new casting.

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