Friction Stir Welding of Dissimilar Al 6061-T6 to AISI 316 Stainless Steel: Microstructure and Mechanical Properties

Abstract

The friction stir welding (FSW) process was recently developed to overcome the difficulty of welding non-ferrous alloys and steels. In this study, dissimilar butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel were welded by FSW using different processing parameters. The grain structure and precipitates at the different welded zones of the various joints were intensively characterized by the electron backscattering diffraction technique (EBSD). Subsequently, the FSWed joints were tensile tested to examine the mechanical strength compared with that of the base metals. The micro-indentation hardness measurements were conducted to reveal the mechanical responses of the different zones in the joint. The EBSD results of the microstructural evolution showed that a significant continuous dynamic recrystallization (CDRX) occurred in the stir zone (SZ) of the Al side, which was mainly composed of the weak metal, Al, and fragmentations of the steel. However, the steel underwent severe deformation and discontinuous dynamic recrystallization (DDRX). The FSW rotation speed increased the ultimate tensile strength (UTS) from 126 MPa at a rotation speed of 300 RPM to 162 MPa at a rotation speed of 500 RPM. The tensile failure occurred at the SZ on the Al side for all specimens. The impact of the microstructure change in the FSW zones was significantly pronounced in the micro-indentation hardness measurements. This was presumably attributed to the promotion of various strengthening mechanisms, such as grain refinement due to DRX (CDRX or DDRX), the appearance of intermetallic compounds, and strain hardening. The aluminum side underwent recrystallization as a result of the heat input in the SZ, but the stainless steel side did not experience recrystallization due to inadequate heat input, resulting in grain deformation instead.

Exploring the Potential Application of an Innovative Post-Weld Finishing Method in Butt-Welded Joints of Stainless Steels and Aluminum Alloys

“…Article [13] aimed to evaluate the impact of different parameters in the tungsten inert gas (TIG) welding process on mechanical properties, stitch width, and microstructural characteristics of welds compared to 316 steel. Reference [14] discusses diverse butt joints between 6061-T6 aluminum alloy and AISI 316 stainless steel fabricated through friction stir welding (FSW) with varying parameters. The studies cited as [15] examined aluminum-magnesium (Al-Mg) alloys, particularly alloy AW 5083 and its joints using both MIG arc welding and FSW methods.…”

A Review of Optimization and Measurement Techniques of the Friction Stir Welding (FSW) Process

“…Cylindrical threaded Medium-carbon steel [97] AA6061-T6 and Ti6Al4V Cylindrical and tapered WC with 10% Co [98] Pure titanium (CP-Ti) and Ti6Al4V sheets Truncated conical [47] Al 6061-T6 to AISi 316 stainless steel Cylindrical WC-Co [99] AA1050 and AZ91 Cylindrical H13 steel [100] AA6061-T6 and pure Cu Cylindrical --- [101] Pure Al-pure Cu Cylindrical, tapered, straight triangle, and straight square W302 steel [102] Galvanized steel (GS) and mild steel Q235 Conical tapered WC [103] AZ31-AM60 --Tool steel [104] Table 3. FSW machines and characteristics [105].…”

Extrinsic-Riveting Friction Stir Lap Welding of Al/Steel Dissimilar Materials

“…Many methods were proposed to improve the mechanical properties of the joints. Changing to a new experimental design or improving the welding parameters are relatively classic strategies [9][10][11]. Adding an interlayer between the Al alloys and steel can prevent direct contact between the two materials, reducing the production of hard and brittle intermetallic compounds (IMCs) [12][13][14].…”