Effect of PWHT Variables on Microstructure and Mechanical Properties of the Al-Zn Weld Metal

In this investigation the microstructure and mechanical properties of Al-Zn (Al 7075) MIG weld metal were studied in respect to T5 post weld heat treatment variables. Samples were cut from butt weld which were produced by automatic MIG welding with the same heat treatment in different times (10 to 480 minute) and temperatures (85 to 225 C o ). The mechanical test results showed that the optimum mechanical properties (as: tensile and yield strength, impact energy and hardness) gained in 155 C o and 120 minute. XRD, Optical metallographic and EDX point analysis results of the sample with best mechanical properties (155 ̊C - 120min) showed that the microstructure consists of fine grain above 15 μm diameter with 15% precipitate, in addition the precipitates were distributed at the grains and grains boundary, at the grains boundary Al2Mg3Zn3 and in the grains CuAl2 were precipitated.