Preparation And Microstructure And Properties Of M40 Continuous Carbon Fiber Reinforced Magnesium Matrix Composites

Here,carbon fiber reinforced magnesium matrix composites were prepared by pressure impregnation method using AZ91 D magnesium alloy as the matrix and M40 carbon fiber as reinforcement,The influence of different preparation processes on the microstructure and mechanical properties of the composites was studied;The influence of interface on mechanical properties was also studied;Finally,ultrasonic C scanning and X ray three dimensional microscopy were used to detect the defects in the composites,and the effect of defects on the mechanical properties of the composites was studied.The study shows that when the infiltration temperature is 750?,the bending strength of M40/AZ91 D composites reaches the highest 1408 MPa when the preheating temperature is 550?,and the bending strength of the preheating temperature is 500?and 450?is 1257 MPa and 1007 MPa,respectively.The higher the preheating temperature,the smaller the temperature difference between the surface of the fiber and the impregnated melt,which reduces the thermal stress;When the preheating temperature of the preform is 550?,the bending strength of the M40/AZ91 D composite material reaches the highest at the temperature of 760?when the melt infiltration temperature of the magnesium alloy increases,which is 1793 MPa.The bending strength of the centigrade is 1408 MPa and 1042 MPa respectively when the infiltration temperature is750?and 780?.The higher the infiltration temperature,the longer the infiltration time for the melt,and the bending strength of the lower part is nearly half lower than that in the upper part,Because the lower matrix alloy is not enough to infiltrate the existing part of the solidification,and the mechanical properties of the composite near the graphite side are generally high then one side close to alloy.A small amount of needle like Al₄C₃ and massive Mg₁₇Al₁₂2 phase were found at the interface of M40/AZ91 D composite.The bonding strength of the interface was moderate;and a large number of thicker interface products like needle which mainly containing Y and massive A_l5Mg₁₁Zn₄ precipitates were found at the interface of M40/AZ91D?Y?composite,and the interface reactions are so voilent that interfacial bonding was easily brittle fracture and the more interfacial reactions due to the reduction of mechanical properties of the composites.The ultrasonic C scan needs to make the artificial defects to make the contrast.The sensitivity of the layer defect detection in the composite material is high,and the defects with the size of more than 100?m can be detected;The ultrasonic C scanning plane diagram can determine the specific size and position coordinates of the defects,and the three-dimensional 4D diagram can know the distribution of the defects in the composite material,but it can not intuitively know the specific type of the defect;The X ray three-dimensional microscope according to the different absorptivity of X ray in the different structure of the object to reconstruct the internal structure in three dimensions by 360degrees-scanning.The defects in the internal structure can be clearly defined,and the defect type in the composite can be directly determined.The X ray three-dimensional microscope can clearly detect the wire cutting of M40/AZ91 D composites,and the size of the cracks about 5?m can be detected,which is more accurate than the C scanning.