Work

Integrated process-structure–property–performance optimization of cold-sprayed zinc coatings on AZ91 magnesium alloy

Year: 2025

Type: article

Abstract: • An optimum range of cold spray parameters was identified for cold spray depositing Zn on AZ91. • This optimum range resulted in ∼200 µm/pass deposition, <0.5 % porosity, greater than 30 MPa adhesion strengths, two-fold decrease in wear rate and the formation of a metallurgical bond at the interface. • Corrosion potential, current and resistance measurements indicated improved performance of the Zn coating over uncoated AZ91. Long term hydrogen evolution measurements showed that the coating outperformed existing industrial coatings in salt water environments. • Smoothed particle hydrodynamics model was used to rationalize the formation of an optimal range of parameters and to reveal the temperature and plastic strain evolution during the cold spray process. High-pressure die cast (HPDC) AZ91 magnesium alloy is widely used in automotive components such as transmission housings and brackets for its excellent strength-to-weight ratio. Zinc-based cold spray coatings can be applied selectively to vulnerable areas to enhance corrosion resistance, minimize galvanic coupling with dissimilar metals, and eliminate the need for full-surface oxide coatings, making the process more efficient and targeted. A comprehensive evaluation of 16 combinations of nitrogen carrier gas temperatures and pressures led to the identification of an optimal range of process parameters, yielding Zn coatings with porosity <0.5 % by area, wear rates reduced by a factor of two compared to uncoated AZ91, and adhesion strengths up to 35 MPa. The enhanced mechanical performance of the coating is attributed to the low porosity and the formation of a metallurgical bond at the coating-substrate interface. Corrosion studies using macroscale potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) revealed a significant decrease in corrosion rate and a shift to more noble corrosion potentials (ZCP) for coated substrates. Furthermore, the Zn cold-sprayed samples exhibited significantly lower corrosion-induced evolved hydrogen content compared to the base AZ91 substrate and AZ91 coated with industrial coatings, demonstrating that the Zn layer effectively protects the substrate from the corrosive environment. Overall, cold spray Zn coatings significantly improve the mechanical and corrosion performance of AZ91 Mg alloys, addressing key material challenges and enabling their broader use in automotive applications.

Source: Journal of Magnesium and Alloys

DOI: 10.1016/j.jma.2025.09.005