The Research On Friction And Wear Behaviour Of Magnesium Borate (Aluminium Borate) Whisker Reinforced Magesium Matrix Composites

For its high specific strength, excellent specific modulus and damping properties, Magnesium alloys is potential material for application in automotive and aerospace industries.However, up to now, because of its hardness and wear resistance is not big, it can not be used in certain situation which has special requirement. It can most efficiently improve the hardness and wear resistance of Magnesium alloy and still keep it's other goodness, that is add reinforcments to Magnesium alloy. And which has been becoming one of the most active areas in materials study field. Metal matrix composites present great promises and opportunities for a new generation of materials.The micrographs reveal reasonably uniform distribution and random orientation of the Mg₂B₂O₅ or Al₁₈B₄O₃₃ whiskers in the as cast composite fabricated by Vacuum-Gas Pressure Infiltration process casting. The hardness, elastic modulus and tensile strength of the Mg₂B₂O₅w/AZ91D composite were increased significantly compared to magnesium matrix alloys. The lubricated and unlubricated sliding friction and wear behavior of Mg₂B₂O₅w/AZ91D composite was evaluated under different loads and sliding speed on a pin-on-disc wear-testing machine MS-T3000. The wear mechanism also was analyzed.The conclusion for the Mg₂B₂O₅w/AZ91D composite under lubricated sliding condition was as follows:Wear can be divided into two periods according to friction coefficient fluctuating for the composite sliding: Run-in period and Stead-going period. Compared to matrix alloy, at low loads the fluctuating of the composite is less, and so is its value.A critical load was observed for the composite at a constant sliding speed. Above which the wear transited from mild into severe wear. And the composite exhibited improved wear resistance when the test loads lower than the critical loads. Which became worse when the test loads were higher. The critical loads shift to lower value with increasing in sliding speed, 25 N, 18 N, 10 N and 5 N were found for sliding speed 1 m/s, 2 m/s, 3 m/s and 5 m/s, respectively.The activation of the severe wear is to have relation with the product of load (P) and sliding speed (V). A critical PV value 36 kgm²s^-3 is calculated for the composite under lubricated sliding condition. Abrasion and delamination were found to the dominant mechanism for the mild and severe wear period respectively by Scanning Electron Microscopy (SEM) and X-ray diffraction analysis (XRD) .Otherwise, the tribology and wear behavior were also studied for the Mg₂B₂O₅w/AZ91D composites under dry sliding condition and Al₁₈B₄O₃₃W/AZ9ID composite under lubricated sliding condition, respectively. The wear mechanism was also analyzed.