Investigating ion nitriding for the reduction of dissolution and soldering in die-casting shot sleeves

As liquid aluminum at 780 °C is pored into the horizontal shot sleeve of a die casting machine, the surface gets washed out by the molten stream exposing the die steel to chemical dissolution and soldering, which leads to failure. This paper investigates the efficacy of ion nitriding surface treatment for preventing surface dissolution and soldering. Cylindrical coupons with various nitriding depths are dipped in hot liquid aluminum melt for a predetermined time. The amount of soldered metal and the weight loss due to dissolution was measured. Ion nitriding is shown to significantly reduce both of these wear modes at shorter dip times, with larger reductions seen for deeper nitrided case depths. Also, ejection tests were done on a casting solidified on the nitrided pin and the force of ejection was measured. It is found that ion nitriding significantly reduces this force, which is a surrogate measure of wettability and adhesion.