中文摘要：

本文通过超声疲劳试验方法研究了超声冲击处理对两种铝合金（AA6061和AA7075）搅拌摩擦焊接头超高周疲劳行为（10^7-10^9周次）的影响。利用微观组织、显微硬度以及X射线衍等方法对表面处理技术对试样表层材料的作用进行了表征。结果显示,超声冲击处理可以在接头表面形成强化层,使疲劳裂纹源由试样表面转移至内部。对铝合金AA6061,接头处理前后疲劳强度差异不大,但可明显提高AA7075接头的疲劳寿命。最后,对疲劳裂纹萌生的特点和表面强化层以及残余应力对疲劳强度的作用机制进行了分析。

英文摘要：

The effect of ultrasonic peening treatment （LIPT） on very high cycle （10^7- 10^9 cycles） fatigue behavior of friction stir welded joint in two aluminum alloys （AA6061 and AA7075） was studied based on ultrasonic fatigue experiment. The effect of surface treatment technology on sample surface plastic deformation layer was characterized by microstructure observation, micro hardness testing and X-ray diffraction. Results indicate that ultrasonic peening treatment can form a hardened layer to enhance the joint surface and make the transformation of fatigue crack source from sample surface to internal part. For aluminum alloy AA6061, the effect of UPT on joint fatigue strength is not significant, but the fatigue life of alloy AA7075 joint can be improved obviously. Finally, the characteristics of fatigue crack initiation and the mechanism of surface hardening layer and residual stress on fatigue strength were analyzed.