Effect of Heat Input Conditions on Microstructure and Mechanical Properties of Friction-Stir-Welded Pure Copper

Abstract

Defect-free friction stir welds of 5-mm-thick pure copper plates were produced in relatively low heat input conditions. The characteristics of the microstructure and mechanical properties of the welded joints were investigated. The stir zone (SZ) exhibited equiaxed recrystallized grains, whose size decreased as the heat input was decreased. The percentage of high-angle grain boundaries (grain boundary misorientation angle >15 deg) in the SZ was quite high (90.2 to 94.5 pct) and increased as the heat input was increased. When the heat input was decreased, the percentage of the twin boundaries (TBs) dropped, and the number of the twin lamellas was reduced. Under a very low heat input condition, the typical characteristics of thermomechanically affected zone (TMAZ) were discernible; however, the TMAZ was characterized by a recrystallized grain structure at higher heat input conditions. The grains in the heat-affected zone (HAZ) were slightly coarsened compared to those in the parent material (PM), but the grain size varied a little under different parameters. The hardness of the SZ increased as the heat input was increased, and the lowest hardness appeared at the HAZs where the welds failed. The ultimate tensile strength (UTS) was similar to that of the PM under various heat input conditions, but the yield strength (YS) and elongation were lower. The YS increased as the lowest hardness value increased, and the elongation decreased due to the enhanced strain localization.

Optimum Rotation Speed for the Friction Stir Welding of Pure Copper

“…However, tensile strength of specimens with increasing of rotation speed to 1200 rpm showed a little variation. In the FSW joints, the HAZ and the TMAZ are critical zones so that, these zones often have the minimum hardness, and fracture initiates from these regions [2,8,13]. A sudden change in the hardness can also result in weakening of these zones, and fracture occurs.…”

“…Xue et al [8] investigated FSW of the copper plates with the thickness of 5 mm in the 1/2H condition. They conducted two different experimental tests, that is, one in the constant traverse speed of 50 mm/min with different rotation speed of 400, 600, and 800 rpm and the other with the constant rotation speed of 800 rpm and different traverse speeds of 50, 100, and 200 mm/min.…”

The influences of rotational and welding speeds on microstructures and mechanical properties of friction stir welded Al5083 and commercially pure copper sheets lap joints

“…Also pure copper welded joints are widely used in nuclear industries and vacuum devices. Because of copper's high thermal conductivity, conventional fusion welding methods of its alloys need high heat input and cause many defects like high distortion, large Heat Affected Zone (HAZ) and significant residual stresses [21].…”

Effect of welding parameters on microstructure and mechanical properties of friction stir welded Al–Mg–Er alloy

“…FSW parameters such as rotation rate, welding speed, tool geometry, and joint design have obvious influences on the material flow and heat input [7]. Among these parameters, the rotation rate and welding speed are the most important parameters that affect the mechanical properties of the joints [8].…”