闭孔CNTs/Al复合泡沫搅拌摩擦焊工艺研究

Study on friction stir welding process of closed-cell CNTs/Al composite foam

摘要:

闭孔Al复合泡沫作为一种典型轻质高强材料，在汽车及航空航天领域具有明确需求牵引和应用前景。采用传统方法制备泡沫铝时，生产工艺复杂、样品尺寸受限，严重阻碍了大规模生产。本文提出基于搅拌摩擦焊制备闭孔CNTs/Al复合泡沫新工艺，解决制备大面积闭孔复合泡沫的难题。利用扫描电镜对不同焊接旋转速度的闭孔CNTs/Al复合泡沫预制体及复合泡沫的微观组织进行分析；采用红外线测温仪对焊接过程中预制体温度分布进行研究。利用电子万能试验机对纯Al泡沫和不同孔隙率闭孔泡沫的屈服应力和平台应力进行对比。研究结果表明：当搅拌头旋转速度为1000rpm时，闭孔CNTs/Al复合泡沫预制体表面平滑而致密。同时，增强体CNTs均匀分布在复合泡沫预制体横截面上。在发泡温度650℃，680℃和700℃对比可知，最佳发泡温度为680℃发泡15min，泡孔结构均匀，孔隙趋于圆形，最大泡孔直径为0.48mm。常温压缩时，闭孔复合泡沫的应力-应变曲线表现出脆性与韧性相结合的变形特征。孔隙率为30.5%时，闭孔泡沫的屈服应力和平台应力值最大。同时，与纯Al泡沫相比，闭孔泡沫的屈服应力提高了2-2.8倍；平台应力提高了1.4-2.9倍。

Abstract:

Closed-cell Al composite foam with high specific strength and high specific stiffness is a typical lightweight material, which has broad application prospectsSin the fields of automobile and aerospaceSapplication. However, the pore structure of aluminum foams prepared by traditional methods is difficult to control, which seriously hinders the production. In this paper, a new preparation process for closed-cell CNTs/Al composite foam based on friction stir welding was proposed. The microstructure and elemental composition of the CNTs/Al composite foams with different rotationSspeeds (1000-1300rpm) were analyzed by scanning electron microscopy and energy dispersive analysis (SEM/EDS). The temperature distribution of the CNTs/Al precursor foam was studied by infrared thermometer and numerical simulation. The mechanical properties of pure Al foam and the CNTs/Al composite foam with different porosity were compared and analyzed by the quasi-static compression test. The results show that when the rotary speed of the stirring is 1000rpm, the surface of the CNTs/Al precursor foam is smooth and dense. Simultaneously, a blowing agent TiH₂, a stabilization agent Al₂O₃ and reinforcedSphase CNTs are uniformly distributed on the cross section of the composite foam. The comparison between the foaming temperature of 680℃ and 700℃ shows that when the foaming temperature is 680℃ for 15min, the pore structure is uniform and mainly consists of circular pores. TheSmaximum pore diameterSisS0.48mm. Infrared thermometer and numerical simulation temperature field show that the temperature gradually decreases with the increase of the distance to the center of the stirring head, and the peak welding temperature is located in the stirring head which exhibits aSbowl-shaped distribution. The stress-strain curves of the CNTs/Al composite foam show the deformation characteristics combining brittleness and ductility at room temperature. When the porosity is 30.5%, the yield stress and platform stress values of the CNTs/Al composite foam are the largest. Compared with the pure Al foam, the yield stress of the CNTs/Al composite foam is increased by about 2-2.8 times, and the platform stress is increased by about 1.4-2.9 times.