Effect Of Rare Earth Oxides On Microstructure And Properties Of In-situ Particulate Reinforced Aluminum Matrix Composites Fabricated By Friction Stir Processing

In this paper,the Ni/Al composites were fabricated by Friction Stir Processing?FSP?with 1060 Al as the base material.The effects of rare earth oxides on microsteucture and properties of Ni/Al composites were studied by adding different contents?1-7wt%?and different kinds of ReO?La₂O₃,CeO₂?.The influence of ReO on the in situ reaction was explored,and the microsteucture and properties of?Ni+ReO?/Al composites were researched before and after heat treatment.The experimental results show that: The distribution of Al₃Ni reinforced phase particles becomes relatively uniform in composites and the content of Al₃Ni is the highest when the content of La₂O₃ or CeO₂ is 5wt%.The massive Ni agglomerates of the composites are decreased,and the tensile strength of?Ni+La₂O₃?/Al and?Ni+CeO₂?/Al composites can reach 221 MPa and 238 MPa respectively.Compared with the Ni/Al composites?166MPa?.The tensile strength has increased by 33.1% and 43.3% respectively.However,if the content of La₂O₃ or CeO₂ increases to 7wt%,the situation has gone different: The content of Al₃Ni reinforced phase particles decreases and the massive Ni agglomerates reappear.The tensile strength of?Ni+La₂O₃?/Al and?Ni+CeO₂?/Al composites decreases to 205 MPa,201MPa respectively.Therefore,the best addition of ReO is 5wt% in this experiment.Compared with the Ni/Al composites,?Ni+Re O?/Al composites not only has the the conventional agglomerates types: polymerization shape,long strip shape,leaves texture shape,but also has the newly formed agglomerates types: semi-polymerization shape,inverted C shape,particle-dense shape.La₂O₃ or CeO₂ hinders the adsorption and aggregation behavior of Ni powder in FSP,so that the Ni powder can not be welded together to promote the Al-Ni in situ reaction and form new agglomerates types.In addition,ReO reacts with the matrix and releases large amounts of heat.Therefore,the temperature of composite zone rises and the volume fraction of Al₃Ni enhanced phase increases.The sequence of phase transformations in the heat treatment experiment is: Al+Ni?Al₃Ni+Al+Ni?Al₃Ni+Al₃Ni₂,and the final products are the mixture of Al₃Ni and Al₃Ni₂.After the heat treatment,the thickness of strengthening layer in Ni/Al and?Ni+ReO?/Al composites increases,the new phase Al₃Ni₂ is formed,however the density of Ni agglomerates in?Ni+ReO?/Al composites becomes poor.The tensile strength of Ni/Al composites has decreased by 7.2%,16.9%,23.5% respectively;The tensile strength of?Ni+5wt%La₂O₃?/Al composites has decreased by 21.7%,26.2%,33.9% respectively;The tensile strength of?Ni+5wt%CeO₂?/Al composites has decreased by 18.5%,24.8%,31.5% respectively.