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engyong Bu, Mohammed Yandouzi, Chen Lu, and Bertrand Jodoin (Submitted August 28, 2011; in revised form March 19, 2012) Commercially pure aluminum (CP-Al) powder was deposited by the cold spray process onto AZ91D magnesium (Mg) substrates that had been subjected to three different heat-treatment conditions: namely, as-cast (F), homogenized (T4), and artificially aged (T6). The substrate hardness was measured to be 80.7 ± 1.8, 73.7 ± 4.0, and 103.6 ± 7.4 HV0.025 for the F-, T4-, and T6-Mg alloy substrates respectively. Thick (~400 lm) and dense (below 1% porosity) Al coatings have been obtained. After post-deposition heat treatment at 400 C, the intermetallic Mg17Al12 (b) and Al3Mg2 (c) phases with different thicknesses were found to have formed at the coating/substrate interface depending on the holding time. While no significant thickness differences of the intermetallic layers were detected in the cases of F- and T6-AZ91D substrates, thicker layers formed on the T4-AZ91D substrate. It is believed that the higher Al concentration in the T4-AZ91D solid solution within the a-Mg could diffuse and contribute more easily to the growth of the intermetallic phases. The hardness of the b- and c-phase was measured to be 260.5 ± 10.7 HV0.025 and 279.6 ± 13.7 HV0.025, respectively. Shear strength test results revealed lower adhesion strength after heat treatment, which is attributed to the presence of brittle intermetallic layers at the coating/substrate interface.

Keywords

aluminum coating, AZ91D magnesium, cold spray, intermetallic phases, post-heat treatment, shear strength

1. Introduction Magnesium (Mg) alloys are widely used in automotive and aerospace industries for their light weight, high damping resistance, high strength-to-weight ratio, highly specific stiffness and excellent castability and workability (Ref 1-5). However, their poor corrosion performance and low wear resistance increase maintenance costs as well as

This article is an invited paper selected from presentations at the 2011 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Thermal Spray 2011: Proceedings of the International Thermal Spray Conference, Hamburg, Germany, September 27-29, 2011, Basil R. Marple, Arvind Agarwal, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Andre´ McDonald, Ed., ASM International, Materials Park, OH, 2011. Hengyong Bu and Chen Lu, National Engineering Research Center of Light Alloy Net Forming, School of Materials Science and Engineering, Shanghai JiaoTong University, Shanghai 200240, PeopleÕs Republic of China; and Mohammed Yandouzi and Bertrand Jodoin, Mechanical Engineering Department, University of Ottawa, Ottawa, ON K1N 6N5, Canada. Contact e-mail: [email protected].

Journal of Thermal Spray Technology

limit their service life (Ref 1, 2). Using a coating to protect Mg surfaces from the environment is a possible solution. Several traditional coating fabrication methods such as electroplating, chemical plating, PVD,