Electrochemical corrosion of AZ31 magnesium alloy in the NH₄⁺-SO₄²⁻-Cl⁻ environment is studied. Effect of NH₄⁺ overshadows that of Cl⁻ as the (NH₄)₂SO₄ concentration is 0.005 M or higher, yielding an evolution from localized corrosion to uniform corrosion. Acceleration effect of NH₄⁺ can be attributed to that (ⅰ) NH₄⁺ dissolves the inner MgO and hinders the precipitation of Mg(OH)₂ and (ⅱ) the buffering ability of NH₄⁺ provides H⁺, enhances the hydrogen evolution, and expedites the corrosion process. The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments. The severe corrosion and hydrogen process in NH₄⁺-containing solution results in a high H_ads coverage and yields an inductive loop within the low frequency. Meanwhile, SO₄²⁻ is helpful in generating cracked but partially protective corrosion products, while Cl⁻ could broaden the corrosion area beneath the corrosion product.

Corrosion behavior of AZ31 magnesium alloy in NH₄⁺-bearing chloride solution with controlled pH was investigated by weight loss experiment, hydrogen collection, and electrochemical test combined with surface morphology and topography observation. The results show that NH₄⁺ and pH of the solution can affect the corrosion of AZ31 magnesium alloy. The existence of NH₄⁺ affects the formation and dissolution of corrosion products, which makes the protective effect of the corrosion product layer weaker. The change of pH value not only affects the corrosion mechanism of AZ31, but also alters the concentration of NH₄⁺ ions in the solution, which further influences the corrosion product layer of AZ31, and finally makes the corrosion of AZ31 change significantly.