Abstract
Al-Mg-Si (6061-T6) alloy with 0.8 mm thick plate was welded successfully by use of high speed friction stir welding (FSW) technology. The microstructural characteristics and mechanical property of the butt joints prepared by high speed FSW were analyzed in detail, the influence of welding parameters, fixture condition and after welding heat treatment were also explored. The results shown that sound surface topography and defect-free bonding interface were observed in the nugget zone (NZ). The microhardness of the as-welded joint was lower than that of the base metal because of the welding heat effect. Compared with the conventional speed FSW, the number of β-Mg2Si, Al2CuMg and Al8Fe2Si precipitated phases existed in the high speed FSWed NZ increased, which made the microhardness in the NZ improved significantly. The rod-shaped precipitates (Mg2Si) have the greatest influence on the microhardness distributions. The maximum tensile strength of 301.8 MPa, which was 85.8% of the base metal, was obtained at high rotation speed of 8000 rpm and fast welding speed of 1500 mm/min. The tensile strength of the ultra-high speed FSWed butt joints were improved significantly by post-weld artificial aging, with a maximum joint efficiency of 90.4%.
Highlights
As a light-weight material, Heat-treatable 6xxx aluminium alloys thin plates were widely applied in the transportation industry for meeting the increasing demand for reducing weight [1]
For Friction stir welding (FSW) in heat-treatable 6061-T6 aluminium alloy, an important feature is that the conventional speed FSW technique can lead to the dissolution and coarsening of the precipitates in the weld zone, and affect the mechanical properties of the friction stir welded (FSWed) joints
The precipitates size of Mg2Si and Al8Fe2Si in the nugget zone (NZ) obtained at fast welding speed (1500 mm/min) was smaller than that of low transverse speed (300 mm/min) under high rotation speed process
Summary
As a light-weight material, Heat-treatable 6xxx aluminium alloys thin plates were widely applied in the transportation industry for meeting the increasing demand for reducing weight [1]. The 6061-T6 aluminium alloy sheet welding is inevitable, when it is applied as a structural material. In addition to riveting, FSW is considered to be one of the most effective welding methods in joining 6061-T6 aluminium alloy [3]. For FSW in heat-treatable 6061-T6 aluminium alloy, an important feature is that the conventional speed FSW technique can lead to the dissolution and coarsening of the precipitates in the weld zone, and affect the mechanical properties of the friction stir welded (FSWed) joints. In. the FSWed 6061-T6 aluminium alloy joint prepared by higher rotation speed with faster welding speed followed by PWAA. The main purpose of present work is to prepare high mechanical properties of the FSWed Al-Mg-Si alloy thin plate joint using combination of high speed and PWAA. In an effort to investigate the effect of high speed and PWAA on microstructure characteristics and mechanical properties of the FSWed joints, a detailed analysis was done on microstructure evolution in the nugget zone (NZ) and tensile strength change of the joint
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