Microstructure Design And Mechanical Properties Of Al-X-O Heat-Resistant Aluminum Based Composites

Currently,the development strategy under the goal of "double carbon" has further promoted the research of lightweight high-temperature materials,and aluminum alloys become one of the strong candidates for high-temperature materials because of their high specific strength and other advantages.Due to the inevitable coarsening,softening or stabilization of intermetallic compounds and precipitated phases at high temperatures,the high temperature strength of existing heat-resistant aluminum alloys is limited.In this context,in-situ synthesized aluminum matrix composites show great potential and advantages in high temperature properties.The organization of aluminum matrix composites is highly designable because the properties of the material can be adjusted by changing the ratio,shape,scale and configuration of the second phase material.In this paper,aluminum matrix composites with high volume fraction of in-situ intermetallic compounds and ceramic particles were prepared by liquid-solid reaction and hot extrusion process based on Al-X-O system.The microstructure,mechanical properties and fracture behavior of the composites with different systems were studied,which provided new ideas for the preparation of aluminum materials with high strength and heat resistance properties.The main research contents of this paper are as follows:(1)In-situ reaction systems of various oxides with Al were studied,including Al-CuO,AlFe2O3,Al-MnO2,Al-La2O3,Al-B2O3 systems.In all systems,thermally stable reinforcing phases,i.e.,micron-sized Al2Cu,Al13Fe4,Al6Mn,Al11La3,AlB2 and nano-sized Al2O3,were generated by in-situ reactions,thus realizing the preparation of multiphase and multi-scale particle reinforced aluminum matrix composites.In the above-mentioned series of composite materials,the intermetallic compounds are evenly distributed in the aluminum matrix,and the distribution of nano-Al2O3 in the microstructure is slightly agglomerated.After hot extrusion deformation,the second phase particles in the longitudinal section of the above-mentioned composites have a streamline distribution in the extrusion direction,and the matrix grains are generally submicron,for example,the average size of the longitudinal section of(14.7Al2O3+6.9AlB2)/Al composite is 0.74 μm.The results of the mechanical properties tests show that different Al-X-O composites have different characteristics,for example,(3.2Al2O3+9Al13Fe4)/Al composites have a high elongation of 19.2%at room temperature while maintaining the tensile strength of 280 MPa,and the tensile strength of(14.7Al2O3+6.9AlB2)/Al composites can reach 220 MPa at 350℃,but the plasticity is poor.(2)On the basis of the above composite reaction system,the Al-X-O composite system was optimized.According to the characteristics of intermetallic compounds and ceramic particles,three kinds of(Al2O3+Al13Fe4+AlB2)/Al composites were obtained through in-situ reaction by adjusting the contents of Fe2O3 and B2O3.It is found that the average size of the polygonal AlB2 particles is 1～2 μm,the average size of the elongated Al13Fe4 particles is 1～4μm,and the average grain size of α-Al is 0.5～3 μm,and the nano-Al2O3 exhibited a distribution along the grain boundaries.Hot extrusion makes α-Al in the composites form<111>//ED silk texture,and the Al13Fe4 particles form(400)//ED orientation.The high-temperature tensile results show that the strength of the prepared(12.5Al2O3+4.5Al13Fe4+5.3AlB2)/Al composite at 350℃ can reach 235 MPa,and the strength values of the three optimized composites at 350℃can keep above 50%of the room temperature strength values.The strength of(10.5Al2O3+9Al13Fe4+3.5AlB2)/Al composite can still reach 115 MPa at 500℃ It is found that(Al2O3+Al13Fe4+AlB2)/Al composite is ductile fracture at room temperature,and the distribution of Al2O3,Al13Fe4 and AlB2 particles in the aluminum matrix and the grain refinement of the matrix significantly improve the strength of the composite.The fracture of materials at high temperature is a mixed fracture of toughness and brittleness,and the microfracture step includes nucleation,growth and polymerization of pores.