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.