Stress corrosion cracking of magnesium alloy with the slow strain rate technique

Abstract

This chapter examines the stress corrosion cracking (SCC) tests of AZ31B magnesium alloy undertaken in distilled water and sodium chloride (NaCI) solutions using a slow strain rate tensile (SSRT) technique under various potential conditions. SSRT tests are performed at 298 K provided through thermoregulation under open-circuit condition. Electrode potentials during SSRT tests are controlled potentiostatically using a potentiostat, a platinum (Pt) counter electrode, and a saturated calomel reference electrode (SCE). Results are also obtained under cathodically- and intermittently-polarized conditions. After testing, the specimens are examined by scanning electron microscopy (SEM) with no further preparation other than rinsing the specimens in acetone and drying. The results indicate that there is a marked degradation of mechanical properties of the magnesium alloy as a result of its exposure to the 4% NaCI solution at -1.6 V (SCE). SEM results show that many cracks nucleate normally to the tensile axis of specimens and are characterized by transgranular quasi-cleavage appearance. Quasi-cleavage fracture in distilled water is observed at relatively low strain rate. Quasi-cleavage fracture is also observed in chloride solutions, but with corrosion products on the fracture surface that are identified as magnesium hydroxides.