Al-Zn-Mg-Cu铝合金厚板搅拌摩擦焊接头搅拌区微观组织

采用搅拌摩擦焊接(Friction stir welding, FSW)技术对20 mm厚Al-Zn-Mg-Cu铝合金板材进行了焊接,随后采用热电偶、电子背散射衍射技术和透射电镜等手段研究了接头的温度分布和搅拌区沿厚度方向微观组织的不均匀性。结果表明,焊接峰值温度沿板材厚度方向逐渐降低。距焊缝中心10 mm处,板材表面焊接峰值温度最高为430 ℃,板材底面峰值温度最低为302 ℃。温度梯度是导致晶粒尺寸沿厚度方向逐渐减小的主要原因,晶粒细化是连续动态再结晶、不连续动态再结晶和几何动态再结晶综合作用的结果。搅拌区晶粒没有明显的择优取向,且该区域的析出相发生溶解再析出,析出相主要为η′相。

Microstructure of stir zone in friction stir welded joint of Al-Zn-Mg-Cu aluminum alloy thick plate

By using FSW (friction stir welding) technology, a 20 mm thick Al-Zn-Mg-Cu aluminum alloy plate was welded, and then the temperature distribution of the welded joints and the microstructure inhomogeneity in the stir zone along thickness direction were studied by using thermocouple, electron backscatter diffraction technology and transmission electron microscope. The results show that the peak welding temperature gradually decreases along the thickness direction. At 10 mm from the center of weld, the welding peak temperature on the surface of plate is maximum of 430 ℃, and that on the bottom surface of the plate is minimum of 302 ℃. The temperature gradient is the main reason that the grain size gradually decreases along the thickness direction. The grain refinement is the result of the combined effects of continuous dynamic recrystallization, discontinuous dynamic recrystallization and geometric dynamic recrystallization. There is no obvious preferred orientation of grains in the stir zone, and the precipitates in this zone are dissolved and then precipitated, and the precipitates are mainly η′ phase.