Abstract
Diesel engines, characterized by higher breakout pressure and compression ratio in comparison with gasoline engines, require particularly elevated tensile properties for their engine parts. In order to maintain both high strength and high ductility in the cylinder head, i.e., to obtain higher percent elongation without further reducing the tensile strength, AlSi9Cu1 alloy was used to prepare the cylinder head in an aluminum diesel engine. At the same time, the effect of different modification elements, Na or Sr, and Fe content on the reduction of secondary dendrite arm spacing (SDAS) was discussed, and the design of T7 heat treatment parameters were analyzed in order to improve the tensile ductility. The result shows: (1) The SDAS is as small as 18±3 μm for the Sr modified alloy. (2) The percent elongation of the alloy with Sr modification increases by 66.7% and 42.9%, respectively, compared with the unmodified alloy and the alloy with Na modification. (3) Lower Fe content alloy (0.10%) gives good results in percent elongation compared to the alloy with higher Fe content (0.27%); in particular, after Sr modification and T7 heat treatment, the elongation of over 5% is obtained.