Mechanisms of Soldering Formation on Coated Core Pins

Die soldering is one of the major casting defects during the high-pressure die casting (HPDC) process, causing dimensional inaccuracy of the castings and increased downtimes of the HPDC machine. In this study, we analyzed actually failed core pins to determine the mechanism of soldering and its procedures. The results show that the soldering process starts from a local coating failure, involves a series of intermetallic phase formation from reactions between molten aluminum alloys and the H13 steel pin, and accelerates when an aluminum-rich, face-centered cubic (fcc) phase is formed between the intermetallic phases. It is the formation of the aluminum-rich fcc phase in the reaction region that joins the core pin with the casting, resulting in the sticking of the casting to the core pin. When undercuts are formed on the core pin, the ejection of castings from the die will lead to either a core pin failure or damages to the casting being ejected.