空调用电子膨胀阀应力腐蚀外漏原因分析

空调用电子膨胀阀在售后频繁出现外漏失效。采用扫描电镜、能谱分析、断口金相检验等分析方法，发现泄漏以阀体内侧为源，断面呈现沿晶脆性断裂及冰糖状腐蚀特征，析出大量氯化物，在阀体外表形成垂直于焊缝的多处近平行裂纹。金相组织评定显示晶间腐蚀倾向弱，为活化环境下的应力腐蚀失效。追溯制程发现清洗剂变质试验分解出Cl-，将电子膨胀阀浸入可再现售后失效。结合失效机理，制定辅料试验、残留标准，并进行外壳深冲、激光焊接约束拉应力控制，可有效防止故障发生。

Analysis on Stress Corrosion Leakage of Electronic Expansion Valves for Air-conditioners

Leakage failure of electronic expansion valves for air conditioners was detected after sale. To find out the cause, scanning electron microscopy, energy spectrum analysis, and fracture metallographic test were carried out. It was found that the crack initiated from the inside. The fracture surface presented intergranular brittle fracture morphology, rock sugar shaped corrosion characteristic, and an amount of chloride. Several nearly parallel cracks perpendicular to the weld seam were found at the outside surface. Metallographic evaluation showed that the intergranular corrosion tendency was weak. The failure is the stress corrosion in the activated environment. The manufacturing process was analyzed and it was found that chloride ions were decomposed during cleaner deterioration test. The failure can be reproduced. In combination with the failure mechanism, the auxiliary material test and residual standard are developed, and the stress during the shell deep-draw and laser welding is controlled to prevent the failure.