Preparation And Characterization Of Alumina/aluminum Micro-Laminated Composites By MAO-Hot Pressing

Alumina/aluminum composites not only possess the properties of high strength,high modulus and high hardness of alumina ceramic,but also show the good toughness of aluminum metal phase.Therefore,the parts fabricated by the composites exhibit excellent strength and toughness,thereby greatly improving the stability and reliability of the parts in service.And meanwhile they can also meet the light-weight requirements in aviation,aerospace and other application areas.In this paper,alumina/aluminum micro-laminated composites were prepared by MAO-hot pressing method.The composition and microstructure of alumina micro-layer prepared at different MAO times were characterized.The effect of the thickness of alumina layer on the surface roughness,electrical resistivity and breakdown voltage was discussed.Furthermore,the influence of the hot-pressing parameters on the microstructure and density of the alumina/aluminum micro-laminated composite was investigated.The bonding type of the alumina/aluminum interface in composites was also analyzed.In the present work,the aluminum foil(foil A)with a thickness of 50?m was used as a precursor and treated by MAO.As a result,alumina ceramic micro-layer formed on foil surface,obtaining the foil B.Next,foil A and foil B were alternately stacked in a sequence of ABAB……Lastly,the alumina/aluminum micro-laminated composite was prepared by vacuum hot pressing.The composition and micro structure of the alumina micro-layer as well as the alumina/aluminum micro-laminated composite were characterized by use of EDS,XRD,OM and SEM,respectively.The surface roughness of the alumina micro-layer was measured by a roughness meter.The electrical insulating property of alumina micro-layer and the composites were investigated by a dielectric strength tester.The density of the composites was tested by a method based on Archimedes' principle.The results show that alumina ceramic micro-layer generates on foil B by MAO treatment of aluminum foil(foil A).The foil B demonstrates the alumina/aluminum/alumina"sandwich" laminated structure,which could provide two layers of alumina micro-layer as well as one layer of aluminum micro-layer for alumina/aluminum micro-laminated composites.The alumina micro-layer mainly consists of Al and O elements,and at the same time contains a small amount of Si,P.The XRD results indicate that Al and O elements exist mainly in the form of ?-Al2O3.Furthermore,the alumina micro-layer exhibits a porous structure and bonds closely with the aluminum inter-layer.With the prolonging of micro-arc oxidation time,the thickness of the alumina micro-layer increases significantly.For MAO treatment of 15?30min,the obtained alumina layer shows the thickness of 10?15 pm,the surface roughness of 7?12?m,the breakdown voltage of 544?740V,the breakdown time of 21.8?29.6s,and the electrical resistivity of 6.6×1010?7.1×1012?·cm,respectively.The foil B1,whose thickness of the alumina micro-layer is about 10?m,is laminated with the foil A and then prepare alumina/aluminum micro-laminated composites by hot pressing.The optimized parameters of the hot pressing are the hot pressing pressure of 4MPa,the hot pressing temperature of 590?,and the holding time of 40min.The alumina/aluminum micro-laminated composites prepared at these parameters show obviously lamellar structure,such as the 1O-?m-thick alumina layer and the 45-?m-thick aluminum layer,uniform inter-layer spacing,well-bonded interface,and absence of clear pores and cracks.The density of the prepared composites approximates to 2.95g/cm3.The breakdown voltage of the alumina/aluminum micro-laminated composites,prepared at the above optimized hot pressing parameters,elevates as the number of micro-layer increases.When the layer number is 20,the breakdown voltage is 130V;and when the layer number increases to 50,the breakdown voltage reaches 330V.The bonding of alumina/aluminum interface in the micro-laminated composites demonstrates two types.The first one is the alumina/aluminum interface formed by MAO in foil B,namely the micro-metallurgical bonding.The second one was the interface generated by the interlocking of the alumina micro-layer on foil B surface with foil A during hot pressing,which was the mechanical bonding.