Precipitation Behavior and Corrosion Properties of Stirred Zone in FSWed AA5083 Al-Mg Alloy after Sensitization

Abstract

This paper investigated the Mg-rich phase precipitation behavior and the corrosion performance throughout the thickness direction within the stirred zone (SZ) of friction stir welded (FSW) AA5083 alloy after 175 °C/100 h sensitization. For the as-welded SZ, the recrystallized grain size gradually decreased from the top surface (5.5 μm) to the bottom (3.7 μm). The top and bottom of the SZ maintained relatively high levels of deformed grains and accumulated strain induced by either shoulder pressing or pin stirring. After 175 °C/100 h sensitization, 100 nm thick β′-Al3Mg2 precipitates were present along the grain boundaries (GBs) in the SZ. The bottom of the SZ exhibited more continuous precipitates along GBs due to the fine grain size and the large fraction of high-angle grain boundaries (0.724%). Although the as-welded SZ exhibited excellent corrosion resistance, it became extremely vulnerable to intergranular cracking (IGC) and stress corrosion cracking (SCC) after sensitization. The large SCC susceptibility indices of the SZ samples ranged from 66.9% to 73.1%. These findings suggest that sensitization can strongly deteriorate the corrosion resistance of the Al-Mg FSW joint, which is of critical importance for the safety and reliability of marine applications.

Effects of Fe, Si, Cu, and TiB2 Grain Refiner Amounts on the Hot Tearing Susceptibility of 5083, 6061, and 7075 Aluminum Ingots

“…Similar descriptions can be found in ref. [30]. Finally, T-Mg 32 (Al,Zn) 49 dots also form at grain boundaries, contributing to an increased HTS.…”

“…On the basis of the microstructural evidence, this study observed that when a 5083 alloy was subjected to shrinkage-induced thermal stress, the inherently brittle fishbone-shaped IMCs turned into hot tearing nucleation points and fractured [Supplementary Figure S3] (see Supplementary Materials). Once hot tearing had occurred, the continuous-phase Al3Mg2 along the interdendritic spaces became a medium for transmitting and promoting crack growth (e.g., the distribution of Al3Mg2 shown in [Supplementary Figure S4] (see Supplementary Materials)), which may be similar to the role of Al3Mg2 in friction stir welding [30]. Moreover, due to the widely distributed fishbone-shaped α-Al15(Fe,Mn)3Si2 in 5b, continuous fractures such as local pore clusters (Figure 10f) or elongated irregular fracture patterns (Figure 10d) emerged upon crack expansion.…”

Subregion Based Prediction of Residual States in Friction Stir Welding of Dissimilar Metals

“…Mechanical properties in the welding region can be changed by the selected welding technologies, especially when dissimilar materials are involved [21][22][23][24][25]. The mechanical properties, mainly yield strength and tensile strength, generally decrease due to precipitate dissolutions in FSW of aluminum alloys [26][27][28][29]. In FSW of dissimilar metals, changes in mechanical properties becomes more complex [30].…”