Formation and progression of die soldering during high pressure die casting

High pressure die casting experiments have been conducted and detailed metallurgical examination of the soldered samples was made to study the formation and early progression of die soldering. It was found that soldering formed initially with a build-up of cast alloy on the samples (named mechanical soldering). Two major build-up modes were identified. One was a sudden build-up of a thick layer and the other was a more gradual build-up of a comparatively thinner layer. Analyses suggested that local hot cracking contributed to the initially thick build-up while compression and ejection shear provided the condition for the thin layer development. Evidences have shown that, even in the most impinged locations, soldering intermetallics formed and grew (hence metallurgical soldering) at the interface between the cast alloy build-up and tool steel during the subsequent casting cycles through a solid state reaction. An analysis has then been made to explain why mechanical soldering may or may not evolve to metallurgical soldering based on thermodynamic and kinetic considerations.