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Magnesium is the lightest metal used in structural applications, such as aerospace industry, and therefore, it provides the greatest potential for weight or energy reduction. It is particularly suitable for transport technology applications. In order to substitute aluminium alloys in aeronautical engines, wear behaviour of magnesium alloys is considered. A comparison of the unlubricated wear resistance of an aluminium alloy (A 357) and two magnesium alloys (AZ 91 and WE 43) rubbed against 52 100 bearing steel in a pin-on-ring configuration over a range of sliding speed (1 -7 m/s) and applied normal loads (20 -80 N) is established. In addition to the measurement of the friction force and wear depth, the temperature near the sliding contact is also measured using a thermocouple placed at the back of the pin sample. Thermal effect on friction and worn surfaces are observed and characterized. Wear transitions are found for the AZ 91 and the A 357 alloys. These transitions are controlled by critical temperatures at the contact surfaces. Scanning electron microscopy observations and profilometric analyses are conducted to confirm these transitions and identify the wear mechanisms.

Abstract

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In hot-forming processes, the interface tool/product is important for the quality of the finished product surfaces. Consequently, it is important to better understand the phenomena, namely, oxidation, which occurs at the interface between tool and sheet in this kind of process. It is in this context that an experimental program was conducted to analyse friction, wear and oxidation behaviours on the tribological performance of the combination of tool and sheet. A high-temperature pin-on-disc tribometer, with an original open-sliding contact, was used. Pins, representing tools are X40CrMoV5 high-alloyed steel, and discs, representing drawing products, are Fe360B steel plates (EN 10025–S235JRG2). The friction and wear study of the combination was carried out at temperatures ranging from ambient (room temperature) to 800℃ and within a normal load range of 35–140 N. Regarding oxidation effect and wear mechanisms, they are examined and characterized by scanning electron microscope and energy-dispersive X-ray spectrometer. As for the experimental results, they showed that the increase in temperature involves the decrease in the friction coefficient due to the oxide scales for all the tests. Pre-oxidized discs are also tested. It was found that the wear process is characterized by an adhesive wear with a transfer of oxides on the pins.