Effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91-xLa/Nd alloy

Abstract

The effect of La/Nd ratio on microstructure and mechanical properties of as-cast AZ91D alloys were investigated. The alloys were produced by casting the molten metal into a preheated steel mould. Microstructures were investigated by XRD and SEM (equipped with EDS). The hardness measurement was carried out by Brinell hardness (HB) digital display tester. Compression tests were conducted at both room and high temperatures (20 °C and 150 °C). Microstructural characterizations reveal that the area fraction of the β-Mg17Al12 phase changed with the variation of La/Nd ratio. The area fraction of the β-Mg17Al12 phase decrease significantly and then increased slightly with the increase of La/Nd ratio. Besides, the results show that the addition of La and Nd contributed to the formation of needle-like phase Al11RE3. Meanwhile, the Brinell hardness and high-temperature compression properties of this alloy reach the maximum values (67 HB and 330 MPa, respectively) when the La/Nd ratio is 2/3. In this alloy, the amount of Al11RE3 phase is 51/TA and the average length is 69.55 μm. Moreover, a generation model of Al11RE3 is established and the growth mechanism of Al11RE3 is analyzed. This work thus has proved that La/Nd ratio has a great effect on the microstructure and mechanical properties of AZ91.