焊接参数对搅拌摩擦焊2024-T351铝合金焊接接头断裂韧性和疲劳裂纹生长速率的影响（英文）

Influence of welding parameters on fracture toughness and fatigue crack growth rate in friction stir welded nugget of 2024-T351 aluminum alloy joints

在横向速度为8~31.5 mm/min、搅拌速度为400~800 r/min条件下对厚度为8 mm的2024-T351铝合金板进行搅拌摩擦焊接实验。为了考察焊接样品的各项性能,对焊接样品进行金相分析、维氏硬度和XRD(确是残余应力)测试。为了得到样品的残余应力和应力强度因子(SIF),对样品的搅拌摩擦焊接过程进行有限元分析。基于标准测试方法研究焊接样品的断裂和疲劳行为,焊接样品在焊核区出现初始裂纹且裂纹沿焊接方向扩展;同时采用剪切散斑干涉方法对焊接样品的断裂行为进行进一步研究。结果表明:横向速度和搅拌速度影响样品的断裂韧性和疲劳裂纹生长速率。搅拌摩擦焊使样品的最大断裂荷载和断裂韧性降低了18%~49%。较低的横向速度使焊接接头的断裂韧性稍许降低。在较高的横向速度或较低的搅拌速度下,焊接接头缺陷的增加可导致较低的断裂韧性。在较低应力强度因子差值(ΔK≤13 MPa·m^(1/2))条件下,所有焊接样品的疲劳裂纹扩展速率比其基体合金的疲劳裂纹扩展速率慢;而在较高的ΔK值条件下,焊接样品的疲劳裂纹扩展速率比基体合金的疲劳裂纹扩展速率快得多。

Friction stir welding （FSW） was performed on 2024-T351 aluminum alloy plates. Metallographic analysis, Vickers microhardness and XRD tests were conducted to determine the properties of the welded zone. FE simulation of the FSW process was implemented for the different welding conditions to extract the residual stress and stress intensity factor （SIF）. Fracture and fatigue behaviors of the welds which have the initial crack in the nugget zone and the crack orientation along the welding direction, were studied based on standard test methods. Fracture behavior of the welds was also evaluated by shearography method. The results showed that the tool rotational and traverse speeds affect the fracture toughness and fatigue crack growth rate. FSW provides 18%-49% reductions in maximum fracture load and fracture toughness. A slight diminution in fracture toughness of the joints was observed for lower traverse speed of the tool, and at higher traverse or rotational speeds, increasing the probability of defects may contribute to low fracture toughness. Fatigue crack propagation rate of all welds was slower than that of the base metal for low values of stress intensity factor range ΔK （ΔK〈13 MPa·m^1/2）, but is much faster for high values of ΔK.