强电场中LY12CZ合金摩擦焊缝金属变形行为研究

通过测定摩擦焊接过程参数和焊接接头的焊合区及扭转塑变区的测量,推导了电场作用下LY12CZ合金摩擦焊接过程中,初始动态再结晶的热变形条件方程式和准稳定摩擦阶段焊合区金属的塑性流动方程.结果表明随着摩擦界面温度升高、相对旋转速率降低和外加电场强度的增加,产生初始动态再结晶的临界流变应力降低;随着外加电场强度的增大,LY12CZ合金摩擦焊缝金属的应变速率敏感性指数m增大,但在本实验条件下,当电场强度E>522 V/mm时的m值有所降低;LY12CZ合金摩擦焊缝金属发生塑性变形的变形表观激活能随外加电场强度的增大而降低.

On Establishing Physical Model for Friction Welding Process of Aluminum Alloy in External Electric Field

Up to now, to our best knowledge, the behavioral characteristics of metals in electroplastic state have not been fully exploited in friction welding process. NNSFC (National Natural Science Foundation of China) approved (Approval No. 50005017) our application for research support and has supported us since 2000 to establish, as one of several important objectives, the physical model for friction welding process of aluminum alloy under electric field. Section 2 establishes in some detail the kinetic recrystallization model of the friction welding process in external electric field. Subsection 2.1 establishes the relationship, eq. (4), among the initial heat deformation parameters--temperature, stress, and rotation speed--during the initial recrystallization stage. Subsection 2.2 establishes the relationship, eq.(9), among temperature, stress, and strain rate in the quasi steady friction welding stage in external electric field. Section 3 gives experimental results and analyses. Subsection 3.1 points out that the critical flow stress in the initial dynamic recrystallization stage decreases with increasing interface temperature, increasing electric field intensity, and decreasing rotation speed. Subsection 3.2 points out that: (1) the strain rate sensitivity exponent in the quasi steady friction welding stage increases with increasing electric field intensity at low electric field intensity but decreases gradually with increasing electric field intensity when the electric field intensity exceeds 522V/mm (Fig.2); (2) the apparent activiation energy of the weld metal in the quasi steady friction welding stage decreases with increasing electric field intensity (Fig.3). Table 2 gives the specific forms of eqs.(4) and (9) for Chinese aluminum alloy LY12CZ (approximately equivalent to ASTM 2024 ) for four values of external electric field intensity: 0, 261 V/mm,522 V/mm,783 V/mm.