Papers by Author: Jason Lo

Abstract: Magnesium matrix composites have great potential for aerospace and automotive applications due to its low density and superior specific stiffness. The magnesium composites can often be reinforced by either particles or/and fibers. There were certain studies on solidification behaviors of particle-reinforced magnesium composites in the past. However, development of grain structure during the solidification of fibre-reinforced magnesium is barely investigated. In this work, an Al2O3 fiber reinforced magnesium (AM60) matrix composite (AM60/Al2O3,f) was cast. The solidification behavior of the cast AM60/Al2O3,f composite was investigated by computer-based thermal analysis. Optical and scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were employed to examine the occurrence of nucleation and grain refinement involved in solidification of the composite. The results show that the addition of Al2O3 fibers leads to the formation of fine grain structure in the matrix of the AM60/Al2O3,f composite. The refinement of grain structure should be primarily attributed to the restriction of grain growth by the limited cellular space formed in the skeleton of the fiber preform structure instead of the nucleation of primary -Mg phase directly on Al2O3 fibers.

Abstract: The common joining techniques for Mg sheet and die cast alloys such as riveting, friction-stir welding and adhesive bonding all introduce additional challenges for protection in the joining areas. First of all, the sheet products are prone to high rate of corrosion due to surface contamination. Introduction of iron-rich contaminants can be encountered from the friction-stir welding process. Although powder coating on top of conversion pre-treatments is practical for mitigating corrosion, the lap-shear adhesion of such surfaces can be negatively impacted when the adhesively bonded joints are exposed to a corrosion environment. Anodized surfaces are better in terms of their ability to retain adhesion strength, but their resistance to galvanic corrosion is an issue. Development of galvanically compatible coatings for steel rivets will benefit the adaptation of riveting as a joining technology for magnesium.

Abstract: Galvanic corrosion is a particularly important form of corrosion for Mg alloys used in automobiles. Our research work focuses on corrosion protection using cost-effective Cr-free coatings. The top-tanking coatings are found to be effective in preventing general corrosion; some of these coatings are also good for reducing galvanic corrosion and stress corrosion. A practical approach for mitigating galvanic corrosion is to increase the electrolytic resistance between the coated steel and the Mg surfaces. This has been demonstrated in the case of a conversion coating plus a powder coat applied on the surface of a magnesium alloy and in the case of a thin Mylar isolation layer installed between the Mg and the steel surfaces.

Abstract: Canadian researchers are actively engaged in the development of novel cast, wrought and composite materials that are based on Mg. An overview is provided of Canadian research projects for new applications of Mg alloys that are targeted to the growing needs of the automotive sector. The research work described is funded primarily through two federal programs: the Canadian Lightweight Materials Research Initiative, and the Materials and Manufacturing Theme of the AUTO21 Network of Centres of Excellence. It includes work on mechanical and corrosion performance of high-pressure die castings, gravity and low pressure castings using permanent and sand molds, sheet Mg development and magnesium matrix composites. The metallurgical research facilities at the CANMET Materials Technology Laboratory are featured.

Abstract: Traditionally, automotive brake rotors are made with cast iron. Besides having economical advantage, cast iron rotor provides many disadvantages due to its weight, such as reduction in fuel efficiency, increase in green house gas emission, and increase in noise, vibration and hardness. With the development of commercial aluminum composites, composite brake rotors are now manufactured. However, the present commercial composite materials are not specifically made for brake application and there are drawbacks. A major drawback is their poor elevated temperature property. In this paper, the unique properties offered by an aluminum composite for brake application is addressed, and an approach to compensate its properties for brake application is highlighted.