Invar 36合金搅拌摩擦焊焊缝的低温韧性

Fracture toughness of friction stir welded Invar 36 alloy at low temperature

为了研究Invar36合金搅拌摩擦焊焊缝的低温韧性,采用小冲杆试验方法(small punch test)对焊接速度2 mm/s,搅拌头旋转频率200～1 000 r/min的Invar36合金焊缝进行低温(77 K)和室温(298 K)韧性测试.298 K下,所有焊接工艺的焊缝小冲杆试验能均高于母材,焊缝韧性随搅拌头旋转频率的提高而降低.77 K下,搅拌头旋转频率小于等于400 r/min的焊缝的低温韧性明显优于母材.所有焊缝在77 K下的小冲杆试验能均高于298 K下的结果,未发生脆性转变.结果表明,Invar合金搅拌摩擦焊焊缝具有优异的低温韧性,但随着搅拌头旋转频率的提高,焊接热输入增加使焊缝组织粗化,从而导致焊缝韧性降低.

The fracture toughness of friction stir welded Invar36 alloy,obtained with travelling speed of 2 mm/s and rotational speed from 200 r/min to 1 000 r/min,were estimated at low temperature(77 K)by small punch test,and were compared with that at room temperature(298 K)as well.At 298 K,all welds have higher small punch energy than the base material.For the welds acquired with the same welding parameters,the small punch energy tested at 77 K is always higher than the ones at 298 K.The small punch energy of welds trends to increase with decreasing of the rotational speed at both 77 K and 298 K. With rotational speeds equal or less than 400 r/min,the small punch energy of welds is significantly higher than that of the base material at 77 K.The results indicate that the friction stir welds keep excellent ductility at low temperature.With the increase of travelling speed,higher heat input produces a coarser microstructure and leads to the reduction of fracture toughness in the weld.