热处理对ZL205A铝合金焊接接头组织与性能的影响

Effect of Heat Treatment on Microstructure and Properties of ZL205A Aluminum Alloy Welded Joints

目的改善25mm厚ZL205A铝合金TIG堆焊接头的组织性能,提高接头的力学性能并明确接头的强化机制。方法通过光学显微镜、扫描电镜、万能拉伸试验机及硬度计等手段,系统研究了T5热处理前后焊接接头显微组织的演变规律及力学性能特征。结果在未经过T5热处理的焊接接头熔核区晶界处,存在大量呈网状分布的白色物质,经过T5热处理后晶界处的白色物质基本消失。热处理后熔核区晶粒间区分明显,晶界清晰可见,晶粒尺寸为25μm左右。晶界处的白色物质主要是Cu原子偏聚后生成的Al_(2)Cu化合物;热处理后,晶界处的Cu原子经过扩散溶解进入铝基体中,达到固溶强化和第二相强化的效果,使接头拉伸强度从196.8MPa升高为431MPa,接头显微硬度从80HV升高为150HV。热处理前后,接头断口处Al_(2)Cu化合物含量变化显著,在未经过热处理的焊接接头断口处,Al_(2)Cu化合物分布较多;而在经过热处理的接头断口处,Al_(2)Cu化合物仅零星出现。最终,接头的断裂类型呈现脆性和韧性混合的断裂方式。结论经过T5热处理后,ZL205A铝合金TIG堆焊接头组织特征得到改善,力学性能得到明显提升,拉伸性能提升了约119%,硬度提升了约87.5%。

The work aims to improve the microstructure and properties of the 25 mm thick ZL205A aluminum alloy TIG surfacing joint,improve the mechanical properties of the joint,and clarify the joint strengthening mechanism.The microstruc-ture evolution and mechanical properties of the welded joint before and after T5 heat treatment were systematically studied with an optical microscopy,a scanning electron microscopy,an universal tensile testing machine,and a hardness tester.The results indicated that there were a large number of white substances distributed in the grain boundaries of the nugget zone of the welded joint that had not undergone T5 heat treatment.After T5 heat treatment,the white substances at the grain boundaries basically disappeared.After heat treatment,there was a clear distinction between the grains in the nugget zone,and the grain boundaries were clearly visible.The grain size was about 25μm.The white substance at the grain boundary was an Al_(2)Cu compound formed by Cu atom segregation.After heat treatment,Cu atoms at grain boundaries diffused and dissolved into the aluminum matrix.Due to the effect of solid solution strengthening and second phase strengthening,the tensile strength of the joint in-creased from 196.8 MPa to 431 MPa,the microhardness of the joint increased from 80HV to 150HV.Before and after heat treatment,there was a significant change in Al_(2)Cu compounds at the joint fracture.There was a high distribution of Al_(2)Cu com-pounds at the fracture surface of welded joints without heat treatment.Al_(2)Cu compound only appeared sporadically at the frac-ture surface of the joint after heat treatment.Ultimately,the joint after heat treatment exhibited a mixed fracture mode of brittle-ness and toughness.After T5 heat treatment,for ZL205A aluminum alloy TIG surfacing joint,its structure characteristics are improved,and its mechanical properties were significantly improved.Its tensile property was increased by about 119%,and its hardness is increased by about 87.5%.