Intergranular Corrosion Failure in Zn-Al Alloy Solenoid Valve Seats

Extensive cracking was found in a batch of die-cast ZAMAK 3 solenoid valve seats during commissioning of the system in which they were installed. Scanning electron microscopic and chemical analyses conducted on one of the failed valve seats showed that the composition of the alloy was different from that specified. The presence of excess aluminum and lead impurities that had segregated to the grain boundaries, coupled with an inadequate amount of magnesium, resulted in intergranular corrosion and subsequent intergranular failure. Corrosion was accelerated by storage in a humid environment in a coastal area. It was recommended that proper chemical analysis of the zinc-aluminum alloy be carried out as a quality control procedure.