Study On Fabrication Of Mg-Al-Si-RE Heat-resistant Magnesium Alloy And Its Microstructure And Properties

As the lightest metal structure materials in the world,magnesium alloys have many advantages such as high strength,high specific stiffness,strong shock sbsorption performance and good electromagnetic shielding performance,widely applied to the automotive industry,aerospace and electronics industries.However,the high temperature performance of magnesium alloys is exactly terrible,making most of the magnesium alloys used below 120°C,which greatly restricts the application and development of magnesium alloys.Alloying is an effective method to improve the heat resistance of magnesium alloys.It is a common way to obtain AS and AE alloys by adding Si and RE elements.The AS magnesium alloys with low Si content have limited heat resistance and the AS magnesium alloys with high content often have poor mechanical properties.At the same time,AE magnesium alloys are extremely expensive,restricting the application of AS and AE alloys.This paper mainly studied the effect of different addition of Ce,La and Nd on Mg-3Al-2.5Si alloy microstructure and mechanical properties based on the casting Mg-Al-Si-RE alloys.By adjusting the content of element,it can reveals the refinement mechanism of primary Mg₂Si phase.Through the refinement and modification of the alloy structure and the properties of the T6 heat-treated,a new type of heat-resistant magnesium alloy with high Si content can be obtainted.Different contents of Ce,La and Nd were added to Mg-3Al-2.5Si alloy.The microstructure of the alloys was investigated by means of OM,XRD,SEM and TEM.The mechanical properties of the alloys were analyzed by hardness and tensile test.The results have shown that Ce,La and Nd can improve the primary Mg₂Si phase in Mg-3Al-2.5Si alloy.When Ce is added in an amount of 1.0 wt.%,the effect of refining primary Mg₂Si is best.When the content of Ce is increased to 1.5 wt.%,the primary Mg₂Si tends to become larger;the effect of La is related to the La content.When the amount of La added was 1.5wt.%,the metamorphism effect was the best;the effect of Nd metamorphism increased first and then decreased as the Nd content increased,and the metamorphic effect was best when the Nd content was 0.6wt.%..T6 heat treatment was performed on the Mg-3Al-2.5Si-xRE alloys.The results show that the primary Mg₂Si is almost unchanged and the eutectic Mg₂Si is partially spheroidized.The??-Mg₁₇Al₁₂ phase is finely distributed on the alloy matrix and grain boundaries,and the grain boundary of the alloy becomes clearer.T6-treated Mg-3Al-2.5Si-xRE alloys were tested by hardness and normal temperature tensile tests.The results show that after adding Ce,the hardness and tensile properties of the alloy improve with the increase of Ce addition.When the Ce content is 1.0wt.%,the hardness value is the highest and the tensile properties are the best.The addition of Ce is continued.to 1.5wt.%,the hardness and tensile properties of the alloy decreased.After La was added,the hardness and tensile properties of the alloy increased with the increase of La content,and reached the best when the La content was 1.5wt.%.After Nd was added,the hardness and tensile properties of the alloy increased first and then decreased,and reached the best when the amount of Nd was 0.6wt.%.The CeSi₂ phase was found in the Mg-3Al-2.5Si-1.0Ce alloy.The relationship between the CeSi₂ phase and the Mg₂Si phase was analyzed based on the misfit theory.The results show that the misfit of the?001?Ce Si₂//?100?Mg₂Si interface is at least7.46%,which satisfies the core and medium effective conditions satisfying 6%<?<15%.Under certain conditions,the CeSi₂ phase can become a heterogeneous nucleation substrate for Mg₂Si.