激光冲击强化对2524铝合金疲劳寿命的影响

目的探索激光冲击工艺参数对2524铝合金疲劳寿命的影响。方法开展不同激光能量、不同冲击次数下的激光冲击强化实验,测试其残余应力和表面硬度,并进行裂纹扩展实验和显微组织观察。结果激光冲击强化能显著提高材料的表面硬度,且材料的硬度值随着冲击能量和冲击次数的增加而递增,但硬度增长率随冲击次数增多而降低。激光冲击强化在试样表层形成较大的残余压应力,使用6.25 J的激光能量冲击1次,最大残余压应力可达-222MPa,并且残余压应力随着激光能量和冲击次数增加而增加,但冲击强化次数存在阈值。相较于未冲击试样,激光冲击1次的试样的疲劳寿命提升32%,冲击2次的疲劳寿命提升41%。对试样断口进行微观形貌观察,在裂纹长度为28 mm处,未冲击试样、激光冲击1次和冲击2次试样的疲劳条带间距分别为1.06、0.628、0.488μm,裂纹扩展速率分别为1.06×10^-3、6.28×10^-4、4.88×10^-4 mm/N。结论激光冲击强化能显著提高2524铝合金的表面硬度,并在表面产生较大的残余压应力。激光冲击强化能够有效迟滞2524-T3铝合金的疲劳裂纹扩展速率,进而有效延长疲劳寿命。

Effect of Laser Shock Peening on Fatigue Life of 2524 Aluminum Alloy

The work aims to study the influence of laser shock peening(LSP) parameters on the fatigue life of 2524 aluminum alloy. The LSP experiments with different laser energies and different shock times were carried out to test the hardness and the residual stress. Then, the crack propagation experiments and microstructure observations were also conducted. LSP treatment could significantly improve the surface hardness of the material, and the hardness value of the material increased with the increasing of the shock energy and the shock times, but the hardness growth rate decreased with the increasing of the shock times. In addition, LSP treatment formed a large residual compressive stress on the surface of the specimen. Under one shock with laser energy of 6.25 J, the maximum residual compressive stress was-222 MPa. Furthermore, the residual compressive stress increased with the increasing laser energy and shock times. However, there was a threshold for shock times.Compared with the unshocked specimen, the fatigue life of the one-shock specimen and two-shock specimen increased by 32% and 41%, respectively. The microscopic morphology of the fracture of the specimen was observed. In the position with 28 mm crack, the fatigue strip spacing of the unshocked specimen, one-shock specimen and two-shock specimen was 1.06, 0.628 and 0.488 μm, respectively. The crack growth rates were 1.06×10^-3, 6.28×10^-4 and 4.88×10^-4 mm/N, respectively. LSP can significantly improve the surface hardness of 2524 aluminum alloy and produce large residual compressive stress on the surface. LSP can effectively delay the fatigue crack growth rate of 2524 aluminum alloy, thus extending the fatigue life.