Effect Of Rare Earth Nd, Y And Gd On Microstructure And High Temperature Mechanical Properties Of AZ Magnesium Alloys

As the lightest structural metallic materials, magnesium alloys have high specificstrength, high specific stiffness, excellent electro-magnetic shielding ability and heatdispersion, good processing properties and casting properties. Therefore, magnesiumalloys have been extensively applied in automotive, communication and aircraftindusties. However, its lower strength and creep resistance at elevated temperaturecause the poor heat resistance of magnesium alloy, which is the main factor of limitingits application at elevated temperature.In this thesis, the effects of different rare earth Nd, Y and Gd on themicrostructure and high-temperature mechanical properties of AZ91 and AZS1magnesium alloy were studied by using optical microstructure(OM), x-raydiffraction(XRD), scan electric microscopy (SEM)/energy dispersive spectrometer(EDS) and tensile properties test.The results show that, rare earth elements effectively refine grains of AZ91 andAZ81 magnesium alloy, increase room temperature mechanical properties and hightemperature mechanical properties, and improve ductility of alloys. For AZ91 alloywith 1%～4%Nd, with the increase of Nd, the tensile strength of alloy rise at first andthen drop. When the content of Nd is 1%, the tensile strength of alloy reach itsmaximum value at room temperature and 150℃, 247.8MPa and 203.1MParespectively, 10.7% and 29.3% higher than AZ91 without Nd. When the content of Ndis 2%, the elongation of alloy reach maximum at 150℃and 250℃, 10.5% and 13.7%respectively.Rare earth Nd, Y and Gd also can refine the grain of AZ81 magnesium alloy. ForAZ81 alloy with 1%～4%Y, with the increase of Y, the tensile strength and elongationof AZ81 magnesium alloy rise at first and then drop. At room temperature, when thecontent of Y is 2%, the tensile strength and the elongation of alloy reach the maximum value, and the peak value are 277.1MPa and 10.9% respectively. Its room temperaturemechanical is 36.5% higher than AZ81 without Y. At 150~C, when the content of Y is1%, the tensile strength and the elongation of alloy reach maximum value, and thepeak value are 220.7MPa and 12.4% respectively. Its high temperature mechanical is40.1% higher than AZ81 alloy's. For AZ81 alloy with Gd, at room temperature and150℃, the tensile strength of alloy reach maximum value, and the peak value are280.1MPa and 212.7MPa when the content of Gd is 3%, respectively. The elongationis best when the content of Gd is 2%～3%. For AZ81 alloy with Nd and Y(Nd/Y=2:3),the tensile strength of alloy reach maximum value, and the peak value are 282.5MPaand 212.2MPa at room temperature and 150℃when the content of Nd and Y is 2%,respectively, and the elongation is also best.It is considered that rare earth Nd, Y and Gd can effectively improves the tensilestrength and ductility of AZ91 and AZ81 magnesium alloy due to the effects of solid-solution strengthening, precipitation strengthening and fine-grained strengthening.