钛/铝异种合金脉冲激光焊接接头裂纹产生机理

Mechanism of Crack Generation in Pulsed Laser Welded Joint of Titanium/Aluminum Dissimilar Alloy

目的对0.8 mm厚的Ti6Al4V钛合金和2 mm厚的AA6060铝合金薄板进行脉冲激光焊接,分析异种轻合金激光焊接裂纹产生的机理及界面结合机理。方法采用扫描电镜、EDS能谱以及显微硬度计等微观表征分析方法,对焊接接头的形貌特征、成分以及显微硬度进行分析,探索焊接接头处裂纹产生的原因。结果钛/铝脉冲激光焊接性较差,接头存在严重的裂纹缺陷,裂纹多集中在焊缝与铝母材交界处以及焊缝中心区域位置,主要以热裂纹为主;接头焊缝可能存在大量的Ti-Al金属间化合物以及少量未熔的钛,其界面层主要成分推测为层状TiAl和外层锯齿状的TiAl_3;接头整个焊缝区域的平均显微硬度为HV_(0.1)420,其硬度水平远远高于焊缝两侧铝合金母材,也高出钛合金母材很多。结论钛铝金属间化合物使钛铝焊接接头焊缝区脆性增大,另外接头焊缝区存在较大的组织应力、热应力、拉压应力、拘束应力等复杂应力,致使焊缝内存在较严重的裂纹缺陷。

The paper aims to have pulsed laser welding on 0.8 mm thick Ti6Al4V titanium alloy and 2 mm thick AA6060 aluminum alloy sheet to analyze mechanism of interface bonding and crack generation. Several microstructural tests such as scanning electron microscopy(SEM), energy dispersive spectrometer(EDS) and micro-hardness meter were carried out to analyze morphology, composition and micro-hardness of welded joints and explore the sources of crack generation. The serious crack defects of titanium/aluminum welded joints were mainly based on hot cracks, particularly at the junction of the weld and the aluminum base metal and the center of the welding seam. The results indicated that there was a large amount of Ti-Al intermetallic compound and a small amount of un-melted titanium in the joint welding seam. The main components of the interfacial layer were presumed to be layered TiAl and outer serrated TiAl3. The average micro-hardness of the entire welding seam area was HV0.1420. The hardness level of weld joint was much higher than that of the titanium alloy and aluminum alloy base materials on both sides of the welding seam. The intermetallic compound of titanium/aluminum dissimilar alloys increases the brittleness of the welding seam area of the welded joint. In addition, there are many complex residual stresses such as tissue stress, thermal stress, tensile stress, and restraint stress in the welding seam area, resulting in more serious cracks in weld.