Effect of heat treatment process on microstructure and mechanical properties of Al-Si-Mg-Cu alloy
Effect of process parameters such as solution temperature,solution time,aging temperature and aging time on microstructure and mechanical properties of Al-Si-Mg-Cu alloy was studied by means of scanning electron microscopy(SEM),transmission electron microscopy(TEM)and universal tensile testing machine.The results show that when the solution temperature increases from 500 ℃ to 545 ℃,the size of eutectic silicon in the alloy gradually decreases,and the average size of eutectic silicon reaches its minimum at 545℃.When the temperature exceeds 550 ℃,the alloy will experience partial over burning phenomenon.When the solution temperature is 545 ℃,the solution time increases from 2 h to 16 h,the size of eutectic silicon first decreases and then increases with the increase of solution time.When the solution time is 12 h,the average size of eutectic silicon is the smallest.After aging treatment,the hardness of the alloy significantly increases.When the aging temperature increases from 155 ℃ to 185 ℃,the peak aging time decreases from 8 h to 4 h,and the peak hardness of the alloy is the highest when aged at 175 ℃.Only β"phase is observed in the microstructure of the alloy during aging at 155 ℃,while both β"and θ'phases are observed in the microstructure during peak aging above 155 ℃,achieving dual precipitation phase strengthening.The tensile strength of the alloy can reach 365 MPa at 175 ℃ peak aging,but the elongation decreases to 2.1％.Considering the strength and toughness of the alloy comprehensively,the appropriate heat treatment process is 545 ℃×12 h+165 ℃×8 h.
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