Effect of Mg element content on annealing softening resistance and electrical conductivity of Al-2Si-0.8Fe alloy
Effect of Mg element content on microstructure,mechanical properties and electrical conductivity of Al-2Si-0.8Fe alloy was studied by means of optical microscope,scanning electron microscopy,Brinell hardness tester,electronic universal material testing machine and eddy current conductivity tester.The results show that with the increase of Mg element content,the hardness and tensile strength of the as-cast Al-2Si-0.8Fe alloy continuously increase,while the influence on its electrical conductivity is relatively small.When the Mg content increases to 1.5％,the hardness and tensile strength of the as-cast alloy reach their maximum values,which are 77.1 HBW and 190 MPa,respectively.Compared with the hardness(42.3 HBW)and tensile strength(123.5 MPa)of the Al-2Si-0.8Fe alloy,they increase by 82.3％and 53.8％,respectively,while the decrease in electrical conductivity is limited to within 2.9％.After low-temperature annealing treatment,the electrical conductivity of the alloy is improved.When the Mg content exceeds 1％,the hardness of the annealed alloy significantly decreases and annealing softening occurs.When the Mg content is below 1％,the tensile strength and hardness of the annealed alloy do not significantly decrease,reaching 201.7 MPa and 78 HBW,respectively,showing good resistance to annealing softening.After adding a small amount of Mg,the microstructure of the alloy is mainly composed of primary α-Al,eutectic Mg2Si phase and long acicular β-Al5FeSi phase.With the increase of Mg content,a reaction of β-Al5FeSi→π-Al8Mg3FeSi6 occurs,resulting in a decrease in the number of Mg2 Si strengthening phases in the alloy,which cannot compensate for the hardening effect of solid solution strengthening on the hardness of the as-cast alloy,leading to annealing softening phenomenon.
Al-Si based alloyannealing softeningsolidification characteristic curveelectrical conductivity
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