铝合金高速FSW热输入模型及焊缝峰值温度研究

Investigation on Thermal Model and Peak Temperature in High-travel Velocity Friction Stir Welding of Aluminum Alloy

摘要:

将焊接速度大幅度提升至1000 mm/min,在不同焊接转速下(1000~1900 rpm)对3 mm厚退火态7075铝合金薄板进行搅拌摩擦焊接实验,并用高精度红外热像仪测量焊缝温度,研究了焊接转速对焊缝峰值温度、焊缝外观以及接头组织的影响规律。发现当转速低于1600 rpm时,随着转速的升高,焊缝峰值温度逐渐升高,在1600 rpm时达到最高,接近500 ℃,1600 rpm以后,峰值温度在480~495 ℃之间波动,并有轻微下降的趋势,这一结果与已有热输入模型及焊缝峰值温度公式不相符合。此外,综合考虑焊缝表面以及接头微观组织,发现当转速在1400,1500,1600 rpm时,焊接质量达到最佳。对材料摩擦机制进行分析,发现摩擦系数随焊接转速和焊接温度的变化而变化,从而在热输入模型中引入摩擦系数变量,最终建立了稳态焊接时峰值温度与焊接转速的关系公式。

Abstract:

The applications of tailor friction-stirring welded blanks demand the friction stir welding (FSW) be extended to higher welding velocities. Unfortunately FSW has been traditionally applied at linear velocities less than 500 mm/min and welding parameters and thermal modeling researched and developed at low welding velocities do not directly translate to high-speed linear FSW. Therefore, to facilitate production of high volume aluminum FSW components, in this paper 7075-O aluminum alloy rolled plates of 3 mm thickness were friction stir butt welded at a constant high-travel speed of 1000 mm/min and various tool rotary speeds (1000-1900 rpm) as well as the peak temperature of joint was measured by thermal infrared camera. Effects of tool rotary speed on peak temperature and appearance and cross-sections microstructures and mechanical properties of FSW joints were investigated. The results show that peak temperature of joint increases gradually with increasing the tool rotary speed till 1600 rpm and reaches maximum at 1600 rpm,approximately 500℃. Increase of rotation speed more than 1600 rpm brought about fluctuation of peak temperature form 480 to 495℃ and slightly decreasing tendency. This does not consist with the previous thermal modeling and peak temperature function of welding parameters. With an emphasis on weld quality, the experimental results of cross-sections microstructures indicate that the optimum tool rotary speeds are 1400, 1500, 1600 rpm. Analyzing the mechanism of heat generation about friction, an analytical thermal model of high-travel FSW was developed to estimate the peak temperature in which a variable of friction was created in consideration of the properties of coefficient in the material friction.