摘要
The heat treatment process has great effects on microstructure and conductivity of ingots. In this study, the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting(LFEC), and the effect of different homogenization processes(single-step homogenization at 465 ℃ for different holding times and three-step homogenization) on the microstructure and conductivity of 7075 aluminum alloy were studied by means of metallographic microscopy, electrical conductivity test, differential thermal analysis and X-ray diffraction phase analysis. For comparison, the ingot by conventional direct casting(DC) under the same conditions was also prepared. Results show that the non-equilibrium eutectic phases with low melting point in the ingot dissolve continuously into the matrix as the holding time of single-step homogenization increases. The endothermic peak of non-equilibrium phases can not be completely eliminated through a 24 h single-step homogenization, but can be eliminated after a three-step homogenization(200 ℃/2 h + 460 ℃/6 h + 480 ℃/12 h). Meanwhile, the homogenization has a better effect on the LFEC ingot than the conventional DC ingot. Under the same homogenizing conditions, the grains of LFEC ingot are characterized by a lower content of low melting point phases and the ingot shows higher electrical conductivity than DC ingot.
The heat treatment process has great effects on microstructure and conductivity of ingots.In this study,the ingots of high strength 7075 aluminum alloy were prepared by low frequency electromagnetic casting （LFEC）,and the effect of different homogenization processes （single-step homogenization at 465 ℃ for different holding times and three-step homogenization） on the microstructure and conductivity of 7075 aluminum alloy were studied by means of metallographic microscopy,electrical conductivity test,differential thermal analysis and X-ray diffraction phase analysis.For comparison,the ingot by conventional direct casting （DC） under the same conditions was also prepared.Results show that the non-equilibrium eutectic phases with low melting point in the ingot dissolve continuously into the matrix as the holding time of single-step homogenization increases.The endothermic peak of non-equilibrium phases can not be completely eliminated through a 24 h single-step homogenization,but can be eliminated after a three-step homogenization （200 ℃/2 h ＋ 460 ℃/6 h ＋ 480 ℃/12 h）.Meanwhile,the homogenization has a better effect on the LFEC ingot than the conventional DC ingot.Under the same homogenizing conditions,the grains of LFEC ingot are characterized by a lower content of low melting point phases and the ingot shows higher electrical conductivity than DC ingot.
基金
financially supported by the National Natural Science Foundation of China(youth)(No.51004036)
the Fundamental Research Funds(N120309002)
