The Influence of Pre- and Post-Heat Treatment on Mechanical Properties and Microstructures in Friction Stir Welding of Dissimilar Age-Hardenable Aluminum Alloys

Abstract

An Al-Mg-Si alloy 6061 and an Al-Zn-Mg alloy 7A52 were joined by friction stir welding successfully. Pre- and post- heat treatment were employed to improve the strength of the weld. The results show a best weld joint with the lowest hardness of 100 HV in 6061 matrix, being achieved by post-solid-solution and subsequent two-stage artificial aging for the whole weld joint of the 7A52 and 6061 solid solution. Under this condition, the weld nugget zone (WNZ) is stronger than 6061 matrix but it has lower hardness than 7A52 matrix. The hardness of WNZ is contributed by the combination of η′ and L precipitates, dynamically changes along with the ratios between the number of η′ and L precipitates. The higher the number density of η′ precipitates, the hardness of WNZ is closer to that of the 7A52 matrix. Otherwise, the higher number density of L precipitates, the hardness of WNZ is closer to that of 6061 matrix. The coexistence of η′ and L precipitates is a direct result from the mixture of 7A52 and 6061 alloys achieved by stirring. Precipitates identification and composition analysis reveal a dynamic WNZ with constituent transition in hardness and composition.

Heat Input and Mechanical Properties Investigation of Friction Stir Welded AA5083/AA5754 and AA5083/AA7020

“…It can be observed that both profiles show almost no reduction in the base materials hardness in all the heat affected zone of the two alloys; however, a slight increase in the hardness of the AA7020 alloy can be observed towards the NG center regardless of its position at the AS or RS. This can be attributed to the solid solution strengthening that can occur due to the stirring of the dissimilar alloys [41]. On the other hand, there is a slight decrease in the hardness of the AA5083 towards the NG center regardless of its position at the RS or the AS.…”

“…The tensile strength properties of the FSW joints are usually compared with those of the alloy having lower tensile strength [41][42][43]; here AA5083. For design purposes, the yield stress is used more frequently than the ultimate tensile strength so that the yield stress is determined (σ 0.2% ) for the tested base materials and FSW joints.…”

Friction Stir Welded AA5052-H32 under Dissimilar Pin Profile and Preheat Temperature: Microstructural Observations and Mechanical Properties

“…The increased preheating temperature resulted in coarser grain size, which resulted in a small loss in both tensile strength and joint hardness. Moreover, the influence of pre-and post-heat treatment on the hardness of Al alloy weld joints (7A52 and 6061) was explored by Jia et al [32], and the effects of preheating and water cooling on the thermal, mechanical, metallurgical, and texture properties of friction-stir-welded AA6082 were investigated by Verma et al [33]. It was observed that preheating has more of an impact on microhardness due to dynamic recrystallization.…”

High-Speed Deformation of Pinless FSWed Thin Sheets in AA6082 Alloy

“…Some researchers focused on the post-welded formability of FSWed lightweight alloys [12,13]. Yang et al studied the effect of pre-and post-heat treatment on mechanical properties and microstructures in friction stir welding of dissimilar age-hardenable aluminum alloys [14]. Cabibbo et al developed an innovative approach to the FSW process of AA5754 blanks, characterized by a welding motion of the pin tool obtained by the combination of two different movements occurring simultaneously, and studied the influence of annealing, prior and after welding [15].…”