铜管连续挤压焊缝形成过程的组织和性能演变

Microstructure and Property Evolution of Weld Seam in Copper Tube During Continuous Extrusion Process

摘要:

利用光学显微镜（OM），扫描电镜（SEM），透射电镜（TEM）和万能电子拉伸试验机对矩形不等壁厚铜管连续挤压焊缝的形成过程进行了研究。结果表明：铜管连续挤压焊缝由2条细晶带汇合而成，晶粒尺寸在13.1~53.4 μm之间，随着挤压的进行，细小晶粒逐渐长大到与基体晶粒尺寸相同，分布在100~200 μm之间，经过模具的压缩区后，发生二次晶粒细化，焊合界面上的微孔消失；挤压焊合过程中发生了动态再结晶，通过位错迁移突破两股金属之间的界面，形成新的晶粒；沿金属的流动方向，焊缝结合强度不断提高，由初始汇合区的63 MPa升高到模具出口处的212 MPa，达到无焊缝区域抗拉强度的98.1%；焊缝断口内的韧窝数量逐渐增多、尺寸增大，延伸率由0.5%升高到35%，达到无焊缝区域的70%。

Abstract:

The formation of weld seams in the rectangular section of continuously extruded copper tubes with unequal wall thickness was investigated via optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and universal electronic tensile testing machine. Results show that the weld seams are formed by the confluence of two fine grain belts with a grain size of 13.1~53.4 μm. As the continuous extrusion proceeds, the fine grains gradually grow to the similar grain size (100~200 μm) of the base material. Secondary grain refinement occurs as the fine grains pass through the compression zone of the die. Afterward, micropores in the welded interface disappear. Dynamic recrystallization occurs during continuous extrusion welding. The interface between the two metal is broken through dislocation migration, and new grains form. The bonding strength of the weld seams dramatically increases along the flow direction of the metal. The bonding strength increases from 63 MPa in the initial confluence area to 212 MPa at the outlet of the die, which achieves 98.1% of that of the weld seam-free zone. The number and size of dimples in the fracture of the weld seams gradually and simultaneously increase. The elongation increases from 0.5% to 35%, reaching 70% of that of the weld seam-free zone.