Fatigue crack growth in the welding nuggetof FSW joints of a 6060 aluminum alloy
Friction stir welded butt joints were performed on 8 mm thick sheets made of AA6060 T6 aluminum alloy by means of a CNC machine tool, at feed rates between 117 and 683 mm/min and tool rotational speed between 838 and 1262 rpm.
利用数控机床进行搅拌摩擦焊将8mm厚的AA6060 T6铝合金对接，进给速度为117~683mm/min，工具转速为 838~1262 rpm。
Tensile tests, metallographic analyses and micro-Vickers tests were carried out to evaluate the mechanical properties of the joints as a function of the process parameters.
The fatigue behavior was studied by means of crack growth tests performed according to ASTM E647 standard on CT specimens, with propagation in the middle of joint along the weld nugget.
The results show the influence of welding process parameters on mechanical properties and fatigue behavior.
Reduction of UTS of about 20–30% with respect to base material occurred with rupture in the softened zone of welding, usually HAZ.
In this range, slight variations of joint efficiency were observed with f/S ratio, while the width of the softening area increases for decreasing values of this parameter.
Fatigue crack growth was always slower thanthat in the base material at low △K below 12 MPa m1/2. The effect of non-optimal welding parameterswas evident at intermediate and high △K, due to defects,such as tunnels, that cause dramatic increase of propagation rate up to fivetimes higher than the base material.
当△K小于12 MPa m1/2时，焊接试样的疲劳裂纹扩展速率总是小于母材的。△K处于中等和较高水平时，焊接试样的疲劳裂纹扩展速率是母材的5倍。这是由于非优化的焊接工艺产生了各种缺陷（比如隧道状的缺陷）。