Aluminum Alloy Bar Solid Solution Of High-strength B93 Two-stage Aging Process Study

Room temperature tensile testing, hardness and electric conductivity measurement, slow strain rate tension, X-ray diffraction, differential scanning calorimetry, optical microscopy and electron microscopy analysis were selected to investigate the mechanical properties, electrical properties, microstructure and evolution rules of the high strength B93 aluminum alloy at different heat-treatment condition, and the heat-treatment regimens were optimized. The results were analyzed and discussed theoretically. Several conclusions can be summarized as follows:1. There are mainly three kinds of second phases in B93 aluminum alloy bar:Al7Cu2Fe,η(MgZn2) and T(AlZnMgCu), which aggregated along the extrusion direction. After the solid solution,ηand T phases were dissolved into matrix evidently, while the Al7Cu2Fe phase could not dissolve and remain to be massive.2. The degree of super-saturation of the basal body increases and the compositions of the solid solution become more homogeneous gradually when the solution temperature elevates or the time extends. However, the grains grew obviously and were tend to over burn when the solution temperature exceed 470℃or the solution time more than 40min, which makes the strength of the alloy decreased. Considering the strength and the plasticity of the alloy, the optimum solution treatment is solution at 470℃for 40min. 3. The tensile strength of the studied alloy decreased with the higher quenching temperature or extending quenching transfer time. The tensile strength became worse when the bar was stay at room temperature for a period of time about 2 to 24 hour. The best delay time for this aluminum alloy bar was in 2 hour or between 24and 48h.4. The precipitation phases after two step ageing developed from GP zone to theη' andηphase's period.5. The first step ageing treatment had a main influence on the strength of the bar; however, their influence to the stress corrosion resistance of the bar was little. Compare to it, the second step ageing had little contribution to the strength but had a significant effect on the stress corrosion resistance property, which was due to the formation of coarse intermittent grain boundary precipitation phase together with the appearance of the Precipitation Free Zone.6. The appropriate two-step aging process is 120℃/24h+170℃16h. At this condition, the tensile strength, elongation and electric conductivity of the studied alloy could reaches 510MPa,10% and 22 MS·m-1, respectively. And the alloy could achieve a favorable resistance to stress corrosion, for instance had only 0.08% strength loss when stretching in the NaCl etchant solution.