The detailed precipitation behavior and grain structure in different sub-regions of friction stir welding (FSW) AA6061-T6 joint after post-weld solution and aging treatments were explored. And the effects of microstructural evolution on mechanical properties, macro/micro electrochemical corrosion behavior and stress corrosion cracking behavior were investigated. The inherent microstructural gradients in FSW joint lead to dramatic degradation of mechanical properties and the presence of macro-galvanic effect, with the latter exacerbating anodic dissolution in heat-affected zone (HAZ) induced by micro-galvanic corrosion and inhibiting pitting corrosion in stirred zone (SZ). Post-weld heat treatment (PWHT) causes the formation of matrix precipitates with similar densities in different sub-regions, resulting in optimized precipitate distribution, comprehensive hardness recovery, and diminished macro-galvanic effect. Grain boundary misorientation angle, grain size and pre-existing dislocations synergistically influence the evolution of grain boundary precipitates (GBPs) and precipitation-free zones (PFZs) during the PWHT. As a result, pitting corrosion is the dominant corrosion form in SZ due to the narrowest PFZ width and dispersed GBPs, while intergranular corrosion is caused by continuous GBPs in other sub-regions. This study verified the dominant role of macro-galvanic effect and micro-galvanic effect in the corrosion process of FSW joint and FSW-PWHT joint, respectively. The maximum SCC susceptibility at HAZ in As-FSWed joint is dominated by enhanced anodic dissolution due to macro-galvanic effect. The SCC sensitivity of FSW-PWHT joint is higher than that of FSW joint due to high electrochemical activity and corrosion rate caused by the severe stress concentration between sub-grains and recrystallized grains at the thermomechanical affected zone (TMAZ)/SZ interface.

中文翻译：

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微观结构特性与电流效应的关系，搅拌摩擦焊接头在焊时和热处理条件下的 SCC 行为


探究了搅拌摩擦焊 （FSW） AA6061-T6 接头在焊后固溶和时效处理后不同子区域的详细析出行为和晶粒结构。并研究了微观组织演变对力学性能、宏观/微观电化学腐蚀行为和应力腐蚀开裂行为的影响。FSW 接头中固有的微观结构梯度导致机械性能的急剧下降和宏观电流效应的存在，后者加剧了微电偶腐蚀引起的热影响区 （HAZ） 的阳极溶解，并抑制了搅拌区 （SZ） 中的点蚀。焊后热处理 （PWHT） 导致在不同子区域形成密度相似的基体析出物，从而优化析出物分布、全面硬度恢复和减弱宏观电偶效应。在 PWHT 期间，晶界取向差角、晶粒尺寸和预先存在的位错协同影响晶界析出物 （GBP） 和无沉淀区 （PFZ） 的演变。因此，由于最窄的 PFZ 宽度和分散的 GBPs，点蚀是 SZ 的主要腐蚀形式，而晶间腐蚀是由其他子区域的连续 GBPs 引起的。本研究分别验证了宏观电流效应和微电流效应在 FSW 接头和 FSW-PWHT 接头腐蚀过程中的主导作用。在 As-FSWed 接头中，HAZ 处的最大 SCC 敏感性主要是由于宏观电流效应而增强的阳极溶解。 FSW-PWHT 接头的 SCC 敏感性高于 FSW 接头，这是由于热机械影响区 （TMAZ）/SZ 界面处亚晶粒和再结晶晶粒之间的严重应力集中导致高电化学活性和腐蚀速率。