The Effect Of Heat Treatment On The Properties Of7N01Aluminum Alloy

Abstract:The better mechanical properties of7N01aluminum alloy are being required to meet the high speed development of high-speed rail industry. In recent years, there are many studies about the effects of aging treatment on microstructure and properties of7N01aluminum alloys. Because the alloy is prone to stress corrosion cracking, its application on the train body is limited. It is essential to study the appropriate heat treatment to improve the stress corrosion resistance of the alloy in recent research trend.The purpose of this study is providing foundation for establishing the proper heat treatments in the production of extruded profiles of7N01aluminum alloy. For this the homogenization of the ingot, the two-step and multistage annealing of the hot extruding structural section has been studied by means of tensile test, metallographic microscopy, scanning electron microscopy, transmission electron microscopy and the energy spectrum analysis. It can lay a foundation in the production of7N01alloy by optimizing the main heat treatment condition and establishing perfect technological process. The results are as follows:(1) Extruding temperature has direct influence on the tensile properties and microstructure of the7N01alloy after T5aging. The higher the extruding temperatures are, the higher the tensile properties the alloy will have, and the alloy will have a higher percentage of recry stallization.(2)T6I6annealing will precipitate a large amount of GP zones at the second step aging of65℃/168h so that it decreases the intragranular precipitation size of η’ at the third aging step. The first step short-time aging makes the amount of η precipitation on the grain boundary is small, and the η precipitation on the grain boundary can’t grow because of lacking of Mg、Zn elements which has formed GP zone at the second step aging. In this way T6I6can largely improve the tensile properties and stress corrosion resistance of the alloy compared with regular aging treatments.(3)T6I7can efficiently optimize the distribution of intragranular η’ and η on the grain boundary so that it can obtain good tensile property and stress corrosion resistance. The T6I6-120annealing can maximize the tensile strength but get worst stress corrosion resistance while the T6I7-160annealing have the best stress corrosion resistance with lowest tensile strength. The T6I7-140annealing can obtain good stress corrosion resistance with little loss of strength in a short aging time.