Effect Of Ball Milling Process On Microstructure And Property Of 2024Al Composites Reinforced With Negative Expansion Ceramics ZrMgMo₃O₁₂

2024Al has been widely applied in aerospace and other fields for their low density,high specific strength,good conductivity,good heat conduction and good processing performance.However,the large coefficient of thermal expansion of2024Al limits its application in in precision devices and inertial instruments.For solving above issues,pure negative expansive ceramic ZrMgMo₃O₁₂ powder with an average particle diameter of 1 m and a density of 3.75 g/cm³ were fabricated by solid powder sintering method after ball milling in this study.Then,10 vol.%negative expansion ceramics ZrMgMo₃O₁₂ powder was mixed with 2024Al powders to fabricate 10 vol.%ZrMgMo₃O₁₂/2024Al composites by vacuum hot-press sintering method.The effect of ball milling parameters on the uniformity of mixed powder,the micro-structure,hardness,mechanical properties and the coefficient of thermal expansion of ZrMg Mo₃O₁₂/2024Al composites were investigated.The following results are obtained:?1?The micro-structure of 10 vol.%ZrMgMo₃O₁₂/2024Al composites prepared by vacuum hot press was mainly composed of?-Al matrix,Al₂Cu phase,Al₂CuMg and ZrMgMo₃O₁₂2 reinforcement.Ball milling process affected the mixing uniformity of ZrMgMo₃O₁₂ powder in 2024Al powder and the micro-structure of ZrMgMo₃O₁₂/2024Al composites after hot-press sintering.Long time ball milling at low ball milling speed or short time ball milling at high ball milling speed was benefit to the uniform mixing of powder.The distribution of ZrMgMo₃O₁₂ in 2024Al matrix was uniform while their agglomeration decreased.However,too high milling speed or too long milling time cannot further improve the uniformity of ZrMgMo₃O₁₂reinforcements in 2024Al powder,but caused cold welding of 2024Al particles,which can't further improve the distribution uniformity of ZrMgMo₃O₁₂ in 2024Al matrix of composites.?2?The mechanical properties of 2024Al can not be improved by adding 10vol.%Zr MgMo₃O₁₂ into 2024Al matrix.The hardness of as-sintered 10 vol.%ZrMgMo₃O₁₂/2024Al composites is always lower than that of as sintered 2024Al.It is mainly attributed to the difference of coefficient of thermal expansion between the negative expansive ceramic ZrMgMo₃O₁₂ and 2024Al and the agglomeration of ZrMgMo₃O₁₂ particles in 2024Al matrix.However,long time ball milling at low milling speed or short time ball milling at high milling speed can improve the distribution of ZrMgMo₃O₁₂ particles in 2024Al matrix,which is beneficial to the improvement of the hardness of composite.The optimal ball milling process is ball milling for 4 h at 200 rpm milling speed.?3?Solution-aging treatment can further improve the hardness of 10 vol.%ZrMgMo₃O₁₂/2024Al composites.The optimum heat treatment process of the composites is solution treated at 490°C for 2 h and aged at 195°C for 10 h after water cooling?i.e.,T6 process?.However,the hardness of 10 vol.%ZrMgMo₃O₁₂/2024Al composite is still lower than that of 2024 Al after treated by the optimum heat treatment process.?4?Similar to the effect of milling parameters on the hardness,long time ball milling at low milling speed or short time ball milling at high milling speed improved the compression strength,compression fracture strain and comprehensive mechanical properties of ZrMgMo₃O₁₂/2024Al composite treated by T6 process.Long time ball milling at high milling speed improved little the compression properties of ZrMgMo₃O₁₂/2024Al composites.Under the optimum ball milling parameters of 200 rpm milling speed and 6 h milling time,the compression strength of the composite is more than 930 MPa,the compression fracture strain is more than50%.The ZrMgMo₃O₁₂/2024Al composites has the best comprehensive mechanical properties.?5?Although the addition of 10 vol.%ZrMgMo₃O₁₂ into the 2024Al matrix could not improve the mechanical properties of 2024Al composites,the thermal expansion properties of the composites were obviously improved.The 10 vol.%ZrMgMo₃O₁₂/2024Al composites sintered after ball milling for 6 h at 200 rpm milling speed have the lowest relative length change and the coefficient of thermal expansion.The coefficient of thermal expansion of the composite is only 19.5×10^-6K^-1,which decreased by 18.03%compared with that of 2024Al.Therefore,the mechanical properties and thermal dimension stability of 10 vol.%ZrMgMo₃O₁₂/2024Al composites can be synergicly improved by the ball milling process of 200 rpm ball milling speed and 6 h ball milling time.