Fatigue crack growth in the welding nuggetof FSW joints of a 6060 aluminum alloy

6060鋁合金攪拌摩擦焊焊接接頭的疲勞裂紋擴展行為

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.

利用數控機床進行攪拌摩擦焊將8mm厚的AA6060 T6鋁合金對接，進給速度為117~683mm/min，工具轉速為 838~1262 rpm。

實驗裝置

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.

通過拉伸實驗、金相分析和顯微硬度測試，研究了焊接接頭力學性能與工藝參數之間的關系。

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.

依據ASTM E647標準，采用CT試樣研究了疲勞裂紋在焊核區中心的擴展行為。

CT試樣尺寸

The results show the influence of welding process parameters on mechanical properties and fatigue behavior.

實驗結果給出了焊接工藝參數對該鋁合金力學性能和疲勞行為的影響。

Reduction of UTS of about 20–30% with respect to base material occurred with rupture in the softened zone of welding, usually HAZ.

與母材相比，焊接后的試樣抗拉強度減小了大約20~30%，試樣在軟化區發生斷裂，該區域通常是熱影響區。

焊接接頭組織

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.

不同f/S比（進給速度/工具轉速）下的接頭系數略有波動，軟化區的寬度隨著f/S比的減小而增大。

疲勞裂紋擴展速率

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.

當△K小于12 MPa m1/2時，焊接試樣的疲勞裂紋擴展速率總是小于母材的。△K處于中等和較高水平時，焊接試樣的疲勞裂紋擴展速率是母材的5倍。這是由于非優化的焊接工藝產生了各種缺陷（比如隧道狀的缺陷）。

疲勞斷口形貌