چكيده به لاتين
Nowadays, magnesium and its alloys have attracted many attention in different industries such as aerospace, transport, and medicine due to their unique properties. However, magnesium and its alloys suffer from undesirable properties at elevated temperatures. Indeed, their mechanical properties decrease significantly by increasing the temperature. This reduction could be minimized by adding reinforcing particles with different sizes and types, which would increase magnesium applications as structural parts at high-temperature conditions. In this Thesis, a metal matrix composite has been fabricated by AZ31B magnesium Alloy and nano-sized aluminum oxide particles as the matrix and the reinforcing phase, respectively. Mechanical-magnetic stir casting method and hot extrusion process (as a bulk forming supplementary operation) were used to produce the composite. Despite the importance of high cycle fatigue (HCF) behavior of the magnesium matrix composites at high temperatures, few studies have been carried out in this field. Consequently, HCF of the nanocomposite has been investigated at high temperatures. Moreover, microstructure, microhardness, uniaxial compressive and tensile properties (at different temperatures) have been studied. The results indicated that by increasing the temperature, mechanical properties including yield stress, ultimate tensile strength, and fatigue strength are reduced in both alloy and nanocomposite specimens. Comparing to the alloy samples, the composite samples showed more desirable properties in all the conditions. For example, fatigue strength of the composite specimens at 100ºC and 200ºC were increased about %87 and %67, respectively. Also, scanning electron microscopy showed that by increasing the temperature, ductile fracture would be dominated in the fracture surfaces of the alloy and composite specimens.
