Al-Li合金搅拌摩擦焊搭接接头的疲劳性能

通过疲劳寿命试验、疲劳断口和金相组织分析,研究了Al-Li合金搅拌摩擦焊搭接接头的疲劳性能,分析了接头前进侧热机影响区(TMAZ, Thermal-Mechanically Affected Zone)出现的"钩状缺陷"对其疲劳性能的影响.结果表明,钩状缺陷容易引起裂纹萌生及扩展,减小接头的有效承载板厚,适当缩短搅拌针长度可以改善钩状缺陷,提高接头力学性能.母材与搭接接头的疲劳S-N曲线研究表明:在高疲劳应力下,接头的疲劳寿命接近母材,但随着疲劳应力水平降低,接头的疲劳寿命急剧下降,200万循环周次下的疲劳强度仅达到80 MPa,为母材的35%.

Fatigue property of Al-Li alloy friction stir welded lap joints

Through the fatigue test, fracture characteristic and microstructure analyses, the fatigue property of the Al-Li alloy friction stir welded lap joints and the effect of "hooking defect" appearing at the thermal-mechanically affected zone(TMAZ) of advancing side on the joint fatigue property were studied. The results show that the cracks can easily initiate and extend from the location of hooking defect, leading to the decrease in the "effective sheet thickness"(EST) of material and damage to the joint fatigue behavior. The appropriate reduction of the pin length is proved one way of to improve the defects and mechanical property of joints. Furthermore, the established S-N curves show that the fatigue life of lap joints is close to base metal on the high fatigue stress. As the fatigue stress decreasing, the joint fatigue life sharply declines and the fatigue strength of joints at fatigue life N=2?10⁶ is only 80 MPa, only equivalent to 35% that of base metal.