Influence of Chemical Composition of Mg Alloys on Surface Alloying by Diffusion Coating
- PDF / 1,125,949 Bytes
- 8 Pages / 593.972 x 792 pts Page_size
- 59 Downloads / 187 Views
ION
THE interest in the application of magnesium alloys is increasing constantly because of their high strengthto-weight ratio. Particularly in the automotive and aeronautical industries, the lightness of the material can be used to increase fuel efficiency.[1,2] However, the major weaknesses of relatively low wear and corrosion resistance significantly limits their wider applications. Although addition of alloying elements, such as Zr, Ag, and rare earth, might improve the strength and oxidization resistance, it also increases the cost and scarifies lightness. Hence, surface treatment has been recognized as an effective technique to enhance the surface durability of Mg alloys without changing the properties of the substrates.[3] Although several surface treatment techniques for Mg alloys have been developed in the past few years[4–13] to improve the wear and corrosion resistance of this type of alloys, one relatively new and promising approach is surface alloying by diffusion coating, for example aluminizing.[4,14–18] This process generates an Al-enriched layer on the surface of an Mg alloy substrate through Al atomic diffusion from an outside source at increased temperatures. As a result of reaction diffusion, Mg-Al intermetallic compounds, including b phase (Mg17Al12) and c phase (Mg2Al3), normally form on the surface of the Mg alloy substrate. J. HIRMKE, formerly Research Fellow, with the CRC for Alloy and Solidification Technology (CAST), School of Mechanical and Mining Engineering, The University of Queensland, Brisbane QLD 4072, Australia, is now with Multi-Contact Essen GmbH, Westendstrasse 10, Essen 45143, Germany. M.-X. ZHANG, Associate Professor, is with the CRC for Cast Metals Manufacturing (CAST), and the Division of Materials, School of Engineering, The University of Queensland. Contact e-mail: [email protected] D.H. ST JOHN, Professor and Director, is with the Centre for Advanced Materials Processing and Manufacturing, The University of Queensland, St Lucia, QLD 4072, Australia. Manuscript submitted June 13, 2011. Article published online January 4, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
The formation of a large amount of b phase (Mg17Al12) in this Al-enriched layer not only leads to increase of wear resistance,[17] hardness, and elastic modulus[18] but also significantly improves the corrosion resistance because the b phase can act as an anodic barrier to inhibit the overall corrosion of the alloy.[19,20] Therefore, in the past decade, materials researchers have exerted considerable effort to optimizing this process. Most surface-alloying treatments of Mg alloys with Al are undertaken at temperatures above 703 K (430 °C). In 2000, Shigematsu et al.[21] reported an b enriched alloyed layer on AZ91D alloy obtained through diffusion coating at 723 K (450 °C). Then, Huo et al.[22] used magnetron sputtering to deposit pure Al on an AZ91D substrate followed by annealing at 723 K (450 °C). This results in the formation of an alloyed layer containing a high volume fraction of b phase on the surface of t
Data Loading...
