OPTIMIZATION OF AN ALUMINUM CYLINDER HEAD ALLOY OF THE AlSi7Cu3MnMg TYPE REINFORCED BY ADDITIONS OF PERITECTIC ELEMENTS

Recent trends in engine design aimed at increasing fuel efficiency, lowering emissions, and reducing size all tend to increase the thermo-mechanical loads seen by cylinder heads. Among several approaches which can be used to combat this problem, the use of new alloys with improved elevated temperature properties (namely tensile and creep strengths) is a promising one. In a previous paper,(1) an AlSi7Cu3Mn alloy reinforced by a combination of the peritectic forming elements V, Zr, and Ti was described. This Mg-free alloy, heat treated to a T7 temper, offered an interesting combination of elevated temperature and creep strength but suffered from a relatively low room temperature yield strength and poor low cycle fatigue strength. Hence R&D work was pursued to improve these properties. The present paper describes the final optimized alloy that has evolved out of this work. Adding a small amount of Mg has strongly improved the room temperature properties as well as the creep strength, while allowing the amount of V needed to be reduced without undo loss in creep strength. The 250 to 350C (482-572F) tensile and creep properties of the new alloy are vastly superior to those of the existing Al-Si alloys currently used for cylinder heads.