The Research On The Preparation And Properties Of Al/?Al-B₄C?/Al Layered Composite

Layered composite materials are new kind of materials which combine two different materials as a layered structure.The layered composite not only maintains the performance advantages of raw materials,but also makes up for the deficiency of them.For example,Al/(Al-B4C)/Al layered composite utilize the hard core layer(Al-B4C)and two soft outer layer(Al or A1 alloys)to improve the plasticity of Al-B4C cermet material.Such materials have been generally fabricated by powder metallurgy process,which is suffering on preparation cost and technological complexity.In this study,the author presents an optimized fabrication method consisting of continuous casting and hot rolling.In continuous casting process,pure Al melt and particles mixture were poured into the outer and inner crystallizer,respectively.The interface bonding took place during the contacting of Al melt and mixed powder under the cooling effect of insulated plate.After the casting,a hot-rolling process at 450 ? was carried out by a twin-roller roller machine to obtain the final composite.The method greatly shortened the preparation process and improved the efficiency.High temperature contacting angle measurement instrument was used to investigate the interfacial forming process between A1 and Al-B4C layers.The range of feasible technological parameters,the influence of the B4C size and the addition of alloy element were studied by hot-press process and static casting process.The heat transfer model between different layers,as well as the composite and crystallizer,is also calculated,which is used to optimize parameters of semi-continuous casting process.Compressive test,impact test and projectile impact test were carried out to investigate the interfacial combination of layered composite.The main contents are as follows:The simulation of high temperature contacting angle measurement shows that the metallic melt directly infiltrated into the Al-B4C composite with low density.For the condition of high density composite,the Si in the melt firstly diffused into the Al-B4C composite,and then remelting occurred at the interfacial region,with a result in the infiltration of metallic melt into the composite.The result indicated that a strong metallurgical bonding interface can formed when the metallic melt contacted with the Al-B4C composite,regardless of the density or B4C mass fraction of the composite.That also means in semi-continuous casting with lower density of Al-B4C composite,the Al melt could infiltrate into Al-B4C composite directly to form the interface.The Al/(Al-B4C)/Al layered composite with good quality can be fabricated at 450?,80MPa pressure and 40%B4C mass fraction.The average micro-hardness of Al/(Al-B4C)/Al layered composite inner layer is 114.97HV and the B4C particle evenly distributed in the inner layer.By the static casting fabrication of the Al/(Al-B4C)/Al layered ingot,the A1 melt pouring temperature is 740 ?,B4C mass fraction is 40%,the thickness of ingot is 26mm.When the Al/(Al-B4C)/Al layered plate rolls to 3mm,the clad ratio rise to its maximum value 61.23%and the density of Al/(Al-B4C)/Al layered plate also achieve its maximum value.The investigation of microstructure and properties of Al/(Al-B4C)/Al layered plate with different B4C fraction shows that,the Brinell hardness is negative correlation with the mass fraction of B4C;while the impact absorbing energy is positive correlation.The Brinell hardness of Al/(Al-B4C)/A1 layered plate after the addition of Mg element increased from 48.7HB to 95.3HB.Based on the heat transfer model of A1 melt with Al-B4C composite and A1 melt with crystallizer during semi-continuous casting process,the optimal parameters were calculated as follows:pouring temperature 740 ?,casting speed 80mm/min,heat-insulation material thickness 6mm.These parameters are also verified by experiments,when cooling water flow rate 2.5m3/h,pouring temperature 740? and casting speed 80mm/min,composite ingots without defects can be fabricated.Then the Al/(7075-B4C)/Al layered ingot is rolled from 120mm to 20mm at 450 ?.The composite plate possessed the compressive strength 152MPa,impact absorbing energy 283J,no interlayer cracks were found at the interface during the projectile impact test.