(1. 南昌航空大學 材料科學與工程學院，南昌 330063；2. 江鈴汽車股份有限公司 車架廠，南昌 330001)
摘 要: 采用摩擦點焊對厚度為2 mm的LY12鋁合金進行焊接實驗，分析接頭的顯微組織及力學性能。根據(jù)焊點接頭的組織特征可將其分為塑性區(qū)、動態(tài)靜止層、熱影響區(qū)和母材。結果表明：塑性區(qū)和動態(tài)靜止層的晶粒在熱和力作用下發(fā)生動態(tài)再結晶形成細小的等軸晶，熱影響區(qū)的晶粒在摩擦熱作用下長大變粗；攪拌頭旋轉速度為2 500 r/min，焊接時間為12 s時，可以獲得力學性能較好的焊點，焊點的剪切強度達到9.24 kN；焊點的剪切強度隨攪拌頭旋轉速度的增大而增大，隨焊接時間的延長先增大后減小；塑性區(qū)的顯微硬度較高，但略小于母材，接頭顯微硬度的最小值分布在熱影響區(qū)；焊點熱輸入量較多時，接頭為Ⅰ型斷裂，焊點的剪切強度較高；焊點熱輸入量較少時，接頭為Ⅱ型斷裂，焊點的強度較低。
關鍵字: LY12鋁合金；摩擦點焊；顯微組織；力學性能
（1. School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, China;2. JMC Frame Plant, Jiang Ling Motors Corporation Ltd., Nanchang 330001, China）
Abstract:Friction stir spot welding(FSSW) of LY12 aluminum sheet with thickness of 2 mm were investigated, the joint microstructures and mechanical properties were analyzed. Based on the structure character of the joint, the microstructure of the joint can be divided into plasticity zone, dynamically quiescent layer, heat affected zone and base metal. The results show that the plasticity zone and dynamically quiescent layer become fine equiaxed recrystallisation under the thermo-mechanical effect, the grains in the heat-affected zone grow up because of the effect of friction heat. When the rotation speed is 2 500 r/min and the welding time is 12 s, good joint is achieved, and the tensile shear strength of the joint reaches 9.24 kN. The tensile shear strength of spot increases with increasing tool rotation speed, with increasing welding time, the strength increases first, while then reduces. The microhardness of plasticity zone is high, but is slightly lower than that of the base metal, the minimum value of microhardness is in the heat affected zone. When the energy input of joint is high, the fracture type of spot is mode Ⅰ, and the tensile shear strength is high; on the contrary, when the energy input of joint is less the fracture type of spot is mode Ⅱ, and the strength is low.
Key words: LY12 aluminum alloy; friction stir spot welding(FSSW); microstructure; mechanical properties
