Post-Weld Heat Treatment Effects on Mechanical Properties and Microstructure of AA6061-T6 Butt Joints Made by Friction Stir Welding at Right Angle (RAFSW)

Mahboubeh Momeni,Michel Guillot

doi:10.3390/jmmp3020042

Mahboubeh Momeni, Michel Guillot

Open Access

https://doi.org/10.3390/jmmp3020042

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Abstract

Friction stir welding (FSW) provides users with many advantages over fusion welding techniques. Nevertheless, it is not widely employed in current industry mainly due to high equipment costs and royalties. To overcome these issues, a low-cost FSW technique operated at a right angle, called RAFSW, has recently been developed by our research team. To make the RAFSW technique reliable for potential users, we are going to analyze the effect of various post-weld heat treatments (PWHT) on the mechanical and physical properties of the RAFSW joints. To this end, optimized process parameters are used to weld butt joints of an AA6061-T6 alloy. The joints were characterized using a tensile test, a micro-hardness test, and metallography techniques. The most efficient aging time was obtained for various aging temperatures. Moreover, it was found that artificial aging at 220 °C for 30 min could be used as a fast and cost-effective artificial aging PWHT for the industrial sector. In addition, the repeatability of the PWHTs were demonstrated by studying the effect of waiting time prior to the artificial aging. Finally, it was revealed that a single fast artificial aging process is more beneficial than solubilizing followed by an artificial aging process in terms of tensile properties, consumed time, and cost.

Highlights

Friction stir welding (FSW) has attracted an increasing interest among researchers and industrial sectors over the past two decades [1]
The microstructure of the NZ changes from top to the bottom of the nugget zone
A comprehensive study was done on the effect of natural aging, artificial aging, and T6 heat treatments on the mechanical and physical properties of the butt-welded bars of AA6061-T6 by a recently developed RAFSW technique using low-cost 3-axis machine tools

Summary

Introduction

Friction stir welding (FSW) has attracted an increasing interest among researchers and industrial sectors over the past two decades [1]. To have a cost-effective FSW process, the PI2/REGAL team at Laval University has recently developed a low-cost FSW technique operated at a right angle [9,10,11,12,13,14] In this technique, called RAFSW, common low-cost 3-axis CNC machines, which are used for machining, are utilized for the RAFSW technique too, without any modification of the CNC machines. The generated forces during the process and the process parameters including the tool tilt angle, plunge depth, rotational speed, and traverse speed affect the physical and mechanical properties of the joint, because they control mixing and stirring processes, the amount of generated heat, and the cooling rate during the FSW process [1,6]. It is necessary to investigate and characterize the effect of different natural aging, artificial aging, and solubilizing processes on the RAFSW joints to make the process reliable for industrial use

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