Hot chamber diecasting with Si₃N₄ ceramic injection system: Application to aluminium alloy components

Although hot chamber diecasting is an appropriate technology for producing high quality cast components, there are material limitations; at the process temperature, aluminium alloy erodes the immersed steel shot sleeve and plunger. Attempts have been made to employ a Si₃N₄ ceramic in place of steel. High quality Al hot chamber diecast components can be manufactured in this manner, but long production runs are not possible because failures occur in the ceramic sleeve even after, for example, a few thousand shots. The fracture in the ceramic sleeve is caused by high stresses arising from the plunger galling the sleeve surface owing to penetration of the Al alloy into the gap between the sleeve and plunger. The infiltrated Al alloy has been found to react chemically with the ceramics; silicon in the ceramic reacts with iron particles present as inclusions in the Al alloy. Hence, the purity of the molten Al alloy in the crucible is a significant factor in the production of high quality diecast components. To prevent penetration of the Al alloy, the injection system is cleaned periodically using hydrochloric acid, which dissolves the infiltrated Al alloy. Since etching by HCl can reduce the strength of the ceramic parts, this cleaning process must also be reconsidered. Recommendations to improve the quality of hot chamber diecast Al components are proposed.