What causes soldering in die casting molds?
The sequence of events leading to soldering and degradation of the die surface in Aluminum pressure die casting are outlined below: • The oxide surface on the H13 tool steel is first exothermically reduced with aluminum, e.g, Fe2O3 + 2Al = 2Fe + Al2O3. The generation of heat from this alumino-thermic reduction reaction accelerates this and subsequent reaction stages. • The liquid aluminum reacts with the nascent Fe formed from stage (1) to produce a series of Fe-Al intermetallics, e.g. Fe + Al = FeAl. This reaction is also exothermic, increasing the local temperature of the die surface, which again can accelerate this and subsequent reaction stages. • Stage (2) occurs only when the die temperature is above a certain critical temperature (Tcrit), that generates a liquid reaction product from stage (2) • The brittle Fe-Al based intermetallics formed from stages (2) and (3) break off the die surface leaving a defect in the die surface • The embrittling formation of Fe-Al intermetallics al
