Stress corrosion cracking behavior of TIG welded Al-Mg-Mn-Sc-Zr alloy

Abstract

Al-Mg-Mn-Sc-Zr alloys with excellent weldability have emerged as ideal candidates for aerospace applications. Currently, the investigations on the corrosion behavior of alloys under tungsten inert gas (TIG) welding conditions are insufficient. Here, the stress corrosion cracking (SCC) behavior of base metal (BM) and weld zone (WZ) of TIG welded Al-Mg-Mn-Sc-Zr alloys was investigated by using pre-cracked compact tensile samples immersed in 3.5% NaCl solution. The direct current potential drop (DCPD) method was used to record the crack propagation. The microstructure and fracture morphology of different regions of TIG welded joints were studied by SEM, EBSD and TEM, and the SCC crack propagation mechanism of BM and WZ was analyzed. The results demonstrated that the critical stress intensity factor for stress corrosion cracking (K_ISCC) of BM and WZ was 7.05 MPa·m^1/2 and 11.79 MPa·m^1/2, respectively. Then, the crack propagation rate of BM was faster than that of WZ, and BM was more susceptible to SCC than WZ. Additionally, the fracture mode of the BM mainly exhibited transgranular fracture, while the fracture mode of the WZ mainly exhibited intergranular and transgranular mixed fracture. Moreover, SCC crack propagation was attributed to the combined effect of anodic dissolution and hydrogen embrittlement. This study will provide experimental and theoretical basis for the wide application of TIG welded Al-Mg-Mn-Sc-Zr alloys in aerospace.

Keywords

tungsten inert gas(TIG) welded Al-Mg-Mn-Sc-Zr alloy / SCC / critical stress intensity factor (K_ISCC) / direct current potential drop (DCPD)

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Central South University