Effects Of Ca And Y On Microstructure And Properties Of As-cast AZ91D Magneisum Alloy

In recent years, the application of magnesium alloys as lightweight materials have been expanding in the automobile and electronics industries due to their low density, high specific strength and stiffness, environmentally friendly. As the most broadly used magnesium alloy in industry, AZ91 D has been limited in many fields because of poor mechanical properties in room temperature and especially in elevated temperature.In this paper, rare earth element Y and alkaline earth element Ca are added into AZ91 D magnesium alloy with the help of AIM. The effects of Ca, Y individual and combination addition on as-cast alloy microstructure, room temperature mechanical properties, elevated temperature tensile properties and corrosion resistance are investigated and analyzed.The results show that with the individual addition of Ca and Y, the α-Mg matrix grain is refined and the β-Mg17Al12 is homogenized. The function of Ca is more efficient in low addition amount(0.8wt%), but with the addition increasing, Y is better eventually.With the increasing addition of Ca, the mechanical properties and corrosion resistance increase at first and then decrease. Ca is mainly dissolved into the β-Mg17Al12 phase when addition is not high(0.8Wt%) and by this means alloy mechanical properties are improved. With the 0.4Wt% addition of Ca, elongation and impact toughness at room temperature reach their optimal value, and the tensile strength gets its maximum value in the 0.8Wt%. When the addition of Ca reach 1.2Wt%, the Al2 Ca is found along with the β-Mg17Al12 and these two phases are intervened distribution in the matrix boundary. The emerged of Al2 Ca in the matrix boundary decreases mechanical properties at room temperature, but tensile properties at elevated temperature and corrosion resistance are benefited from it, get their optimal value.With the increasing addition of Y, the mechanical properties increase at first and then decrease. With the 0.8Wt% addition of Y, Al2 Y emerges in the alloy. This rhombus phase is more diffuse than Al2 Ca in distribution and strengthens alloy further.With the 1.2Wt% addition of Y, attributed to the dispersed phase of Al2 Y, the mechanical properties get their optimal value. The addition of Y has significantly improved on corrosion resistance of the alloy, it only has a small drop in 2.0Wt%, but stil1 higher than the matrix alloy and Ca addition groups,The results show that the hardness is proportional to the addition amount of Ca and Y in general.and Y works more efficientlyBased on 1.2Wt% addition of Y, because of different mechanism, the alloy is more homogeneous with the compound addition of Ca. With the increasing addition of Ca, the mechanical properties increase at first and then decrease. Mechanical properties are improved with Ca dissolved into β-Mg17Al12 phase. Elongation and impact toughness at room temperature reach their optimal value with the 0.3Wt% addition of Ca.And room temperature tensile strength, elevated temperature tensile properties get their optimal value with the 0.6Wt% addition of Ca. The mechanical properties rapidly decrease with the further addition of Ca. Meanwhile the corrosion resistance is declined and hardness unable benefited from the addition of Ca.