The Effect of Tungsten Addition on the Hot Tearing Susceptibility of the AlSi5Cu2Mg Alloy

Hot tears are among the most serious casting defects and limit the applicability of Al-Si-Cu-Mg alloys in automotive castings. This work deals with the effect of a graded tungsten addition on the hot tearing susceptibility of the hypoeutectic AlSi5Cu2Mg alloy. Tungsten was introduced through an AlW5 master alloy in nominal additions of 0.05, 0.10 and 0.15 wt.%, corresponding to measured contents of 0.020, 0.044 and 0.075 wt.%. The susceptibility was evaluated using a five-arm restrained casting mould equipped with a load cell and a thermocouple, by three variants of the hot tearing index and by a qualitative evaluation of the load curve and its first derivative. The nominal 0.05 wt.% addition decreased all three indices into the minimal-to-low susceptibility category, whereas higher additions led to a renewed rise, and at 0.15 wt.% the values reached the level of the reference alloy. The qualitative evaluation confirmed this trend. Thermal analysis showed an increase in the liquidus temperature from 615 to 629 °C and a corresponding widening of the solidification interval. The favourable effect of the low addition is attributed to a possible grain refinement of the primary phase, whereas at higher contents the widened solidification interval prevails.