Strengthening effects of Y and Sr on Al–9Si–0.5Mg alloy

In this work, the effects of Y and Sr on the microstructures and the mechanical performances of Al–Si hypoeutectic alloy were investigated. The results indicated that Y element can improve its mechanical properties. After the T6 heat treatment, the 0.2Y reinforced alloy had the optimal mechanical properties including the maximal tensile strength of 344 MPa, the yield strength of 271 MPa, the hardness of 116 HB as well as the elongation of 6.3%. They successively increased by 14.3%, 32.2%, 19.3% and 8.3% compared with those of the unreinforced alloy. The mechanical performances of the Y–Sr reinforced alloys were superior to that of the unreinforced alloy and were less than that of the 0.2Y reinforced alloys. The critical concentration of Sr should be less than 0.03% after adding Y element to further enhance the 0.2Y modified alloy. The decreasing performances of Y–Sr reinforced alloys were due to the poisoning effects, the appearance of the massive structure, the decline of adsorbed hydrogen as well as the increase of the shrinkage porosity. (paper)