镁含量对铝镁合金FSW焊缝共振疲劳寿命的影响

Influence of Magnesium Content on Vibration Fatigue Life of FSW Welds of Al-Mg Alloy

分别对3种不同镁含量铝镁合金进行搅拌摩擦焊接,根据金属平板平面弯曲疲劳试验标准,对试样进行共振频率下振动疲劳寿命测试,并用显微镜观察试样裂缝扩展特征,分析镁含量对搅拌摩擦焊(FSW)焊缝共振疲劳寿命的影响。研究表明:含镁量较低(0.44wt%)的铝镁合金经搅拌摩擦焊后,振动疲劳寿命出现提升,由0.9×105提高至4.1×105;搅拌摩擦试样振动过程产生的滑移带,可有效降低裂缝传播的驱动力,从而提高试样的振动疲劳寿命;较高镁含量(4.32wt%)搅拌摩擦试样的裂缝传播,为穿晶传播和沿晶传播混合模式,是导致其振动疲劳寿命低的原因之一。

Friction stir welding （FSW） was conducted on three kinds of A1-Mg alloy with different magnesium contents. Vibration fatigue life under resonant frequency was tested according to the test standard of plane bending fatigue testing of metal plates. The crack propagation characteristic of the sample was observed with microscope, and the influence of the magnesium content on resonant fatigue life of the FSW sample was also analyzed. Researches show that the resonant fatigue life of the sample with low magnesium content （about 0.44 wt%） increases after FSW, which increases from 0.9×105 to 4.1× 105. The slip band of the FSW sample generated during FSW is beneficial to the reduction of the crack propagating driving force, thereby increasing the vibration fatigue life of the specimen. The crack propagation of high magnesium content （4.32 wt%） sample is a mixed-mode of transgranular and intergranular, which is one of the causes leading to the decrease of vibration fatigue life.