Improving Corrosion and Corrosion-Fatigue Resistance of AZ31B Cast Mg Alloy Using Combined Cold Spray and Top Coatings

Abstract

In this paper, we report the application of zinc phosphate electrostatic-painting top coating on cold sprayed AA7075 leading to a significant improvement in corrosion-fatigue performance. High strength AA7075 powder was sprayed on AZ31B substrate, followed by the application of the top coating. The electrochemical corrosion and corrosion-fatigue tests of the coated and uncoated specimens were performed in 3.5% NaCl solution. Transmission electron microscopy (TEM) analysis showed that a continuous nanolayered mixture of Mg/Al was formed at the cold spray coating/substrate interface leading to high bonding strength. The results showed that the combined coatings improved the corrosion resistance remarkably, and significantly increased the fatigue life, with a fatigue strength of 80 MPa at 107 cycles, as compared to the as-cast specimen. Surface topographic analysis of the corrosion-fatigue-tested specimens demonstrated the presence of deep macro-pits on the cold sprayed AA7075 coating after 3.7 million cycles, while there were no such pits on the top-coated specimens, even after 107 cycles when tested at 30 Hz. The fractographic analysis of the fatigue-fractured specimens showed that the formation of pits allowed the NaCl solution to penetrate in the AZ31B substrate, creating localized corrosion pits resulting in premature failure, which eventually reduced the fatigue life.

Effects of Ti, Ni, and Dual Ti/Ni Plasma Immersion Ion Implantation on the Corrosion and Wear Properties of Magnesium Alloy

“…Magnesium alloys are widely used in many fields because of their light weight, good damping capacity, and recycling potential [1][2][3]. Unfortunately, the corrosion resistance of magnesium alloys in many engineering applications is insufficient [4,5] and methods such as micro-arc oxidation [6,7], laser cladding [8,9], plasma electrolytic oxidation [10,11] and ion implantation [12][13][14][15] have been proposed to improve the corrosion properties.…”

The Role of Ammonium Chloride in the Powder Thermal Diffusion Alloying Process on a Magnesium Alloy

“…To protect magnesium alloys from serious corrosion, various methods are raised. For example, magnesium alloys could be covered with coatings which are much more corrosion resistant [5][6][7].…”

Characterization of Nanolayer Intermetallics Formed in Cold Sprayed Al Powder on Mg Substrate

“…The cold spray (CS) technique, which deposits dense and high-quality coatings on the surface of the Mg-alloy parts, has shown promising results in resolving this problem [7]. It has also been shown that the AA7075-type Al alloy (later will be considered as AA7075) coating on AZ31B-type Mg alloy (later will be considered as AZ31B) significantly improves the fatigue properties of Mg alloy substrate [8,9]. Compared to other coating processes, such as anodizing, vapor deposition, electroplating, conversion coating, etc., CS delivers harder and thicker coatings, which can protect Mg alloys in harsh environments [9,10,11].…”

“…It has also been shown that the AA7075-type Al alloy (later will be considered as AA7075) coating on AZ31B-type Mg alloy (later will be considered as AZ31B) significantly improves the fatigue properties of Mg alloy substrate [8,9]. Compared to other coating processes, such as anodizing, vapor deposition, electroplating, conversion coating, etc., CS delivers harder and thicker coatings, which can protect Mg alloys in harsh environments [9,10,11]. At the same time, conventional plasma spray process presents challenges in depositing pure aluminum powder due to its combustible nature.…”