Study On Heat Treatment And Compression Properties Of Al₂O₃ Fiber Reinforced Magnesium Matrix Composities

Magnesium alloys have broad prospects a excellent lightweight materials.Discontinuous reinforced magnesium matrix composites have been widely studied in recent years due to their excellent load-bearing and strengthening effects.However,most of them focus on manufacturing processes and perfomance testing,There is little research on the heat treatment and corresponding strengthening mechanisms of discontinuous neinforced magnesium matrix composites,especially short fiber reinforced magnesium matrix composites,In this paper,the agi ng evolution process,creep mechanism and strengthening mechanism of Al₂O_3f（18vol.%）/Mg-6Al-1Nd-1Gd composites different heat trentment states（cast state,T4 state,16 state）were analyzed by studying their microstructure and compression properties（compression creep+ conventional compression）.Combined with the calculation results of the shear stress hysteresis model,the stress distrbution state around the fiber and the influence of temperature and other conditions on the mechanical properties of the composites were atudied.A comprehensive analysis was conducted on the failure mechamism of compposite materials,providing new ideas for the design and heat treatmentef short fiber reinforecd magnesium matrix composites,The conclusions obtained are as follows:（1）The introduction of Al₂O₃ fiber can effectively strengthen the matrix,and the hardness of the composite lncreases from 75HV₅₀ to 130.5HV₅₀.After heat treatment,the microstructure of the composites changes significantly.T4 treatment can promote the disolution of β phase and Al₁₁（Nd,Gd）₃ phase,white T6 treatment can proposite their precipitation.Compared with the matrix alloy,the peak aging time of the composite is shourtened from 32h to 24h.During this period,the β-phase change the most obviously,which mainly exists in continuous precipitation and disconitinuous precipitation,and the β-phase growth relationship is competitive with the aging time increasing.（2）Heat trearment is an effectivt way to optimize the creep resistance of composites.Under the conditions of 200’C and 70MPa,the maximum creep strain value and steady creep rate of T6 composites are 0.82%and 9.25×10^-9s^-1,which are 25.45%and 44.61%lower than those of the as-cast composites.The maximum creep strain value and steady creep rate of T4 composites reach 0.5%and 6.94×10^-9s^-1,respectively.（3）Based on the creep data and the observation of microstructure,it can be seen that the creep mechanism of composites is mainly affected by the distribution of fibers and intermetallic compounds.The creep process of T4 and T6 composites is influenced by the interaction of dislocation climbing and grain boundary slip,while T4 composites are also affected by partial dislocation viscous slip.（4）The stress transfer and distribution of short fiber reinforced magnesium matrix composites are mainly affected by fiber bonding,length-diameter ratio and temperature.The stress distribution around the fiber is most affected by temperature,and has an obvious positive correlation.The greater the cohesiveness and temperature,the greater the stress gradient and the more obvious the end stress concentration.（5）Compared with as-cast composites,the compressive properties of heat-treated composites are better.The compressive strength of T4 and T6 composites at room temperature is much higher than that of as-cast composites（239.95MPa and 222.15MPa,respectively）,which are 29.32%and 19.72%higher than that of as-cast composites（185.55MPa）.When the compression temperature is between 100℃ and 200℃,the compression performance of T4 composites is the best.At the macro level,the composite fracture is step-like quasi-cleavage fracture.At the micro level,the Al₂O₃ fiber plays a role in hindering dislocation and crack propagation and inhibiting material deformation,showing obvious pulling out or debonding.The matrix alloy absorbs the energy at the crack tip and achieves the toughening effect,with obvious dimples.Combined with the simulation results and fracture analysis,it can be seen that the failure of composite materials is mainly affected by the stress concentration at the fiber end,and the fiber segment fracture occurs at high temperature.