Magnesium is an attractive structural material due to its very low density. Among the magnesium alloys, the AZ series containing aluminum and zinc as main alloying elements presents good mechanical properties. However, the great challenge to be overcome by these materials is the poor corrosion resistance, consequence of their high surface reactivity with the formation of oxide/hydroxide films, which generally offer low protection. Therefore, to study the surface characteristics of these alloys is very important. In this paper, the surface of AZ31 magnesium alloy is characterized by ellipsometry after exposure to a 0.1 M Na₂SO₄ solution for 3 min, 5 min, 15 min, and 30 min. Through ellipsometric measurements and proper ellipsometric modeling, the thickness of the surface films grown for all cited immersion times could be known. The modeling acknowledges the three-layer surface film is formed for an inner layer composed initially of mixing of MgO and Al₂O₃. As the immersion time progresses until 5 min, the MgO is successively replaced by magnesium hydroxide (Mg(OH)₂), thickening the intermediate layer of the film, which is composed of dense Mg(OH)₂. On the other hand, the outer layer is composed of porous Mg(OH)₂. The total thickness of the film grows in two stages: in the first 5 min, the film experiments a disruptive thickening until 339 nm; between 5 and 30 min, the total thickness evolves from 339 nm to 386 nm.

镁由于其非常低的密度而成为有吸引力的结构材料。在镁合金中，以铝和锌为主要合金元素的AZ系列具有良好的机械性能。然而，这些材料要克服的最大挑战是差的耐腐蚀性，这是由于它们与形成氧化物/氢氧化物膜的表面反应性高而导致的，这通常提供低保护。因此，研究这些合金的表面特性非常重要。本文通过暴露于0.1 M Na ₂ SO ₄后的椭圆偏光法对AZ31镁合金的表面进行了表征。溶液3分钟，5分钟，15分钟和30分钟。通过椭偏测量和适当的椭偏建模，可以知道在所有提到的浸入时间下生长的表面膜的厚度。该模型确认三层表面膜是为最初由MgO和Al ₂ O ₃的混合组成的内层形成的。随着浸没时间的延长，直到5分钟，MgO依次被氢氧化镁（Mg（OH）₂）取代，使薄膜的中间层变厚，该中间层由致密的Mg（OH）_2组成。另一方面，外层由多孔的Mg（OH）_2组成。膜的总厚度分两个阶段生长：在最初的5分钟内，膜进行破坏性的增厚实验，直到339 nm；然后，在5至30分钟之间，总厚度从339 nm演变为386 nm。