真空扩散焊热循环对2A14铝合金接头界面演变的影响

Effect of thermal cycles on interface evolution of vacuum diffusion bonded aluminum alloy 2A14

分别选取500,530,560℃焊接温度,进行2A14铝合金真空扩散焊,保温时间为60 min,焊接压力为4 MPa,真空压力低于3.4×10-3Pa。焊后用扫描电镜(SEM)观察接头的焊合率、界面和母材组织形貌。结果表明,在500℃固溶线以下温度进行2A14铝合金扩散焊时,主要是界面微区塑性变形破碎氧化膜,实现局部微量的金属之间连接,焊合率很低。温度继续升高到530℃,超过固溶线温度,但小于Al-Cu共晶温度时,增加了界面CuAl2相结合机理,焊合率有明显提高。焊接温度在Al-Cu共晶温度以上,达到560℃时,CuAl2相完全溶解并在晶界生成共晶液相。该液相挤压、破碎界面氧化膜,并填充界面微孔,焊接接头界面呈正弦波状界面形貌,因而焊合率显著提高。根据这一分析结果,建立了晶界液相生成与界面氧化膜的破碎模型。

Wrought aluminum alloy 2A14 samples were diffusion bonded at 500 ℃,530 ℃ and 560 ℃ respectively for 60 min under the bonding pressure of 4 MPa and a vacuum pressure lower than 3.4×10-3 Pa.The bonding ratio,the morphologies of the interface and the microstructures of the base metal were examined by scanning electron microscope.The results showed that at 500 ℃ lower than the solid solution line,the interface after welding remained straight as original in which only a little metallurgical bonding points were presented leading to a very low bonding ratio.At 530 ℃ above the solid solution line but below the Al-Cu eutectic point,CuAl2 phase joining additionally contributed to the bonding mechanism hence the bonding ratio increased apparently.When the temperature was further raised to 560 ℃ above the eutectic point,CuAl2 phase dissolved and the eutectic liquid formed at the crystal boundaries.The liquid was then extruded into the interface which crashed the oxidation film and filled the interface voids so that the bonding ratio increased remarkably.Therefore,a wavy bonded interface,composed of crystal boundaries,substituted the original straight interface.Based on the analyses,a model was proposed for liquid phase formation at the crystal boundaries and oxidation film crash.