Effect of Aluminum-Titanium-Boron Based Grain Refiners on AZ91E Magnesium Alloy Grain Size and Microstructure
Vehicle weight in the aerospace and automotive industries directly impacts carbon emissions and fuel efficiency. An increase in the use of magnesium alloys in structural applications to replace aluminum alloys will result in lighter vehicles. However, the strength of magnesium alloys is lower than that of aluminum alloys. Grain refinement can significantly improve the mechanical properties of alloys. This study investigates the refining potential and fading of Al-5Ti-1B and Al-1Ti-3B grain refiners in AZ91E magnesium alloy.
The grain refiners were added at 0.1, 0.2, 0.5 and 1.0 wt.% levels. These alloys were added to the molten AZ91E magnesium alloy at 740C (1364F) and stirred for 30 seconds. To examine fading of the grain refiners, they were allowed to settle for 5, 10 and 20 minutes in the molten magnesium alloy prior to pouring. The prototype castings were characterized using optical microscopy, SEM and TEM.
The average grain size of the base alloy, AZ91E decreased significantly with the addition of the grain refiners. Minimum average grain sizes were obtained using 0.1 wt.% Al-5Ti-1B and 1.0 wt.% Al-1Ti-3B. For both refiners, grain refinement was attributed to TiB2 particles providing nucleating sites and grain growth restriction. In addition, AlB2 particles provided nucleating sites in the case of Al-1Ti-3B refiner.
Proper choice of the type and quantity of grain refiner additions for grain refinement with an understanding of the fading effects will enable improvement of mechanical properties at minimal cost. The improved mechanical properties of these refined magnesium alloys will promote their use for more structurally demanding applications.
Keywordsmagnesium alloys AZ91E grain refinement aluminum-titanium-boron
Unable to display preview. Download preview PDF.
- 1.Avedesian, M.M., “Magnesium and Magnesium Alloys”, ASM International, Materials Park, OH (1999).Google Scholar
- 2.Davies, J.R., “Aluminum and Aluminum Alloys”, ASM International, Materials Park, OH (1993).Google Scholar
- 3.Ramachandran, T.R., Sharma, P.K., Balasubramanian, K., “Grain Refinement of Light Alloys”, Proceedings of the 68thWorld Foundry Congress, pp. 189–193 (2008).Google Scholar
- 4.Campbell, J., “Casting”, Paperback ed., Butterworth-Heinemann, Woburn, MA (1993).Google Scholar
- 6.Emley, E.F., “Principles of Magnesium Technology”, Pergamon Press, London (1966).Google Scholar
- 9.Zhang, M.X., Qian, M., Kelly, P.M., Taylor, J.A., “Application of Edge-to-Edge Matching Model to Grain Refinement in Mg-Al Based Alloys”, Journal of Material Science and Technology, vol. 21, pp. 77–80 (2005).Google Scholar
- 12.Liu, S., Zhang, Y., Han, H., Li, B., “Effect of Mg-TiB2 Master Alloy on the Grain Refinement of AZ91D Magnesium Alloy”, Journal of Alloys and Compounds, Article in Press (2009).Google Scholar
- 18.Vinod Kumar, G.S., Murty, B.S., Chakraborty, M., “Development of an Efficient Grain Refiner for Al-7Si Alloy”, Materials Science and Engineering, vol. A280, pp. 58–61 (2000).Google Scholar
- 19.Kori, S.A., “Studies on the Grain Refinement and Modification of Some Hypoeutectic and Eutectic Al-Si Alloys”, Metallurgical and Materials Engineering, Indian Institute of Technology — Kharagpur. Ph.D Thesis (2000).Google Scholar
- 21.Kellie, J., Wood, J.V., “Reaction Processing in the Metals Industry”, Materials World, vol. 3, no 1, pp. 10–12 (1995).Google Scholar
- 24.Kumar, R., Mahanty, R.K., “Grain Size Control of Magnesium”, British Foundryman, vol. 66, pp. 39–42 (1973).Google Scholar