Investigations on the Dispersion Synthesis of Al3BC Particle and Its Strengthening Mechanisms in Al Alloys

Author:Zhao Yong Feng

Supervisor:liu xiang fa nikhilesh chawla


Degree Year:2019





With the development of industry and increasing demands for lightweight materials with high strengths both in room or elevated temperature,traditional strengthening techniques of Al alloys,such as precipitation strengthening etc.cannot meet the demands yet.Investigations proposed that the yield strength of Al alloys reinforced by aging is in general limited to about 0.7 GPa.The newly-developed techniques,eg.ultrafine crystallization and amorphization,can obtain a strength on the order of 1 GPa.However,they still have the problems like toughness decrease,low high temperature resistance and size limitation etc.Here we presented a new reinforcement strategy for Al alloys,with a new reinforcement of Al3BC,to meet the increasing demands on high strength and high temperature resistance.A novel Al3BC/AI composite with ultra-high strength,high modulus as well as good high temperature resistance was developed.The mechanical behavior of the Al3BC/AI composite was investigated and the strengthening mechanisms of Al3BC on the matrix were illuminated in this work.The success of Al3BC will provide a new idea for choosing reinforcement of metal matrix composites(MMCs),which is expected to revolutionize the development of novel lightweight MMCs with ultra-high strength.The main research contents were as follows:(1)In-situ synthesis of Al3BC particles and their mechanical propertiesA new solid-liquid reaction method for Al3BC synthesis was used to in-situ synthesize the Al3BC particles from Al melts.The size,morphology and distribution of Al3BC particles can be well controlled by adjusting the fabrication parameters.The size can vary from tens of nanometers to several microns;the morphologies can be hexagonal plates,tetrakaidecahedron or hexagonal prisms;the distribution can be homogenous,river-like or networked.In this work,mechanical properties of Al3BC particle have been quantified experientally via nanoindentation and micropillar compression for the first time.The hardness,modulus and compression strength of Al3BC were measured to be 24,332 and 8.7 GPa,respectively.The high mechanical properties of Al3BC particles are the guarantee of them as the reinforcements of Al composites.(2)Fabrication of Al3BC/Al composites and their microstructure controlingAl3BC/Al or Al3BC/6061 composites with a varying fraction from 10%to 75%were successfully fabricated by liquid-solid reaction method and the microstructures were characterized in this work.Microstructure characterization reveals that nano and submicron Al3BC particles distribute homogenously in the A1 matrix.Large amount of dislocations were observed in the matrix around Al3BC particles in all composites.In this work,the preferred orientations of α-Al and Al3BC particles in extruded Al3BC/Al composites were investigated.The α-Al is refined to around 0.5 μm and shows a plate texture expressed as follows:<110>//ND;