Influence of Deep Rolling Process Parameters on Surface Residual Stress of AA7075-T651 Aluminum Alloy Friction Stir Welded Joint

Abstract

Friction stir welding is most commonly used for joining aluminum alloy parts. After welding, residual stresses occurred in the welded joint caused by non-uniform cooling rate. Friction stir welding usually generates tensile residual stress inside the workpiece which affects the strength in addition to the fatigue life of materials. Compressive residual stress usually is beneficial and it can be introduced by mechanical surface treatment methods such as deep rolling, shot peening, laser shock peening, etc. In this research, deep rolling was used for inducing compressive residual stress on surface of friction stir welded joint. The residual stresses values were obtained from X-ray diffraction machine. Influence of three deep rolling process parameters: rolling pressure, rolling speed and rolling offset on surface residual stresses at the welded joint were investigated. Each factor had 2 levels (23 full factorial design). The statistical analysis result showed that the rolling pressure, rolling speed, rolling offset, interaction between rolling pressure and rolling speed, interaction between rolling speed and rolling offset were statistically significant factors, with the most compressive residual stress value approximately -391.6 MPa. The appropriated deep rolling process parameters on surface residual stress of AA7075-T651 aluminum alloy friction stir welded joint were 1) rolling pressure about 150 bar 2) rolling speed about 1,400 mm/min 3) rolling offset about 0.1 mm.

Sequential Effects of Deep Rolling and Post-Weld Heat Treatment on Surface Integrity of AA7075-T651 Aluminum Alloy Friction Stir Welding

“…FSW was done using the Bridgeport Computer Numerical Control (CNC) machine, model VMC500, as shown in Figure 1. The parameters used for the FSW process [25] are shown in Table 3.…”

“…The FSW workpiece was securely fastened to the mechanical clamping device to prevent the workpiece from moving during the DR process, as shown in Figure 4. The conditions used for the DR process [25] are shown in Table 4. The area for deep rolling is 50 mm in width and 150 mm in length and the tool path of the deep-rolling process starts from the lower left corner of the designated area, as shown in Figure 5.…”

Deep Rolling Techniques: A Comprehensive Review of Process Parameters and Impacts on the Material Properties of Commercial Steels

“…The bulk of the studies pertaining to DR were on standard test specimens or similar components because of the obvious limitations of tooling and experimentation for application prototypes. Nevertheless, there are satisfactory efforts available on DR of components such as turbine/compressor blades [104][105][106], aircraft structural components [8,21], axels [107][108][109], shafts [110,111], crankshafts [112][113][114], tension bolts [115], high-strength fasteners and threaded parts [116,117], connecting rod screws [118], torsion bars [119,120], gear tooth [83], roller and thrust bearing race/rings [78,96,121], welded joints [122][123][124][125][126], blanking punch fillets [22], hip implants [26,27], etc. When deep-rolled, all these applications exhibited significant improvement in fatigue performance, which was attributed to substantial strain hardening, higher magnitude and deeper penetration of CRS, tailored surface region microstructure, and increased boundary layer hardness along with an improved surface finish.…”