Effect of Strontium Pretreatment on Magnesium Alloy Evaluated by Immersion Test

Magnesium alloys have gained significant interest as a structural material for automotive and aerospace applications due to its low-density, high durability and decent castability. As a result, these light alloys possess a promising potential. However, the limitation of low corrosion resistance constraint their practical applications. The aim of this paper is to investigate the corrosion behaviour of AZ31 magnesium alloy by conducting immersion test. this test was intended to determine the resistance of a material to an aggressive, aqueous environment by analysing the weight loss of the sample. Three types of sample were prepared namely bare, phosphated and Sr-P pretreated magnesium alloy. The samples were immersed in 3.5 wt.% sodium chloride solution at 25 degrees C for 24 and 72 hours. Moreover, scanning electron microscopy (SEM) was used to observe the surface of coatings and corrosion product on the test samples. The weight loss values are 4.39x10(-2) g/cm(2) and 4.52x10(-2) g/cm(2) for hare, 2.12x10(-2) g/cm(2) and 3.11x10(-2) g/cm(2) for unpretreated, 1.14x1.0(-2)g/cm(2) and 1.17x10(-2) g/cm(2) pretreated samples after immersion for 24 and 72 hours respectively. The findings show the decreased in weight loss values as the sample being treated. It also discovered that the immersion time has an inversely proportional relationship with the corrosion rate. It was observed that pretreated sample have a finer phosphating grain coverage area that improved the corrosion resistance performance.