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Study on Extrusion and Heat Treatments of AJ and AE Series Cast Magnesium Alloys

Author: ZhangYu
Tutor: CuiJianZhong；LeQiChi
School: Northeastern University
Course: Materials Processing Engineering
Keywords: Mg-Al-Sr alloy AE42 alloy microstructure casting extrusion heat treatment mechanical properties
CLC: TG166.4
Type: Master's thesis
Year: 2009
Downloads: 45
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Abstract


Most of magnesium alloy products is produced by casting. However, the malleable magnesium alloys have high strength, ductibility and more diversiform mechanical properties, can meet the demand for diversiform structure, so that it is a good way to improve the structure and properties of the Mg alloys by forming. This work studied the microstructures mechanical properties of AJ and AE magnesium alloys after casting, homogenization, extrusion and T5 heat treatment, The major conclusions were as followings:1. It was found that the as cast grain sizes of Mg-Al-Sr alloy are decided by the content of Sr.The lower the content is, the smaller the grains become. The content of Sr influences the compositions of phases of Mg-Al-Sr alloy ingot.When the content is low, the main precipitated phases areα-Mg,β-Mg17Al12, Al4Sr. The amount ofβ-Mg17Al12 reduces as the content of Sr increases. Mg17Sr12 appears when the content is higher.2. The optimal casting temperature of Mg-4.25A1-4.38RE alloy is at 700℃. The main phases in this alloy includeα-Mg, Al11RE3, Al2Ce and AlMn. The reasonable homogenization of Mg-4.25A1-4.38RE alloy is at 450℃for lOhours.3. Compared with the same chemical composition of die cast alloy, the mechanical properties of Mg-3A1 extruded improved obviously; The mechanical properties of Mg-6Al extruded is higher than that of die cast alloy with the same chemical composition. The mechanical properties of Mg-3Al and Mg-6Al extruded with different content of Sr are obviously different. The hardness of extruded bars of Mg-6Al with different content of Sr are higher than that of Mg-3A1 with the same content of Sr. The hardness of extruded bars of Mg-6Al with the content of 3% of Sr is the highest,55.6HV. The strength of extruded bars of Mg-3A1 with Sr increases and the elongation decreases with increase in content of Sr. The strength of extruded bars of Mg-6A1 with Sr decreases and the elongation increases with increase in content of Sr. The extruded bars of Mg-3A1 alloy with 3% Sr has the optimal mechanical properties, Rm=285MPa, A=18.8%.4. The mechanical properties of extruded bars of Mg-4.25A1-4.38.RE alloy is higher than that of AE44 die cast alloy. Microstructure of Mg-4.25A1-4.38RE alloy is sensitive to the extrusion temperature.The higher the extrusion temperature is, the larger the grain size becomes, which reduce the hardness.When the extrusion temperature increases, the mechanical properties of extruded bars of Mg-4.25A1-4.38RE alloy reduce, the tensile strength of the bars extruded at 150℃is the highest, Rm=260MPa, Rp0.2=181MPa. The elongation of Mg-4.25A1-4.38RE alloy extruded at 250℃is highest, which is 19.7%.5. After aging the strength of extruded bars of Mg-3A1 and Mg-6A1 alloy with Sr decreases when the content of Sr increases. The extruded bars of Mg-3Al with the 3%Sr has the optimal mechanical properties when aged at 200℃for 12h, whose Rm is 280MPa, Rp0.2 is 167MPa and A is 16.7%6. It is found that after aging the hardness of extruded bars of AE42 alloy which is cast in different temperatures are different. The hardness of extruded bar of AE42 alloy cast in low temperature is higher than that of at high temperature. After aging at 200℃for 4h, the extruded bars of AE42 alloy has the optimal mechanical properties, Rm is 250MPa, Rp0.2 is 172MPa and A is 12.8%.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > The heat treatment of non-ferrous metals and their alloys > The heat treatment of magnesium and its alloys
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