Microstructure evolution, mechanical properties and strengthening mechanisms in the hot extruded Si3N4 particle reinforced Al-Cu-Mg composite

Si3N4 particles, with high modulus, hardness and thermal stability, are important reinforced phase candidates in Al matrix composite. In this work, Si3N4 particles were introduced into the 2026 Al alloy by a novel Al-Si-N master alloy and the Si3N4/2026 Al composite was successfully prepared via gravity casting and hot extrusion process. According to the SEM results, the Si3N4 particles tend to distribute at the grain boundary and coexist with the eutectic phases after solidification; however, a Si3N4 particles chain structure appears in the matrix after subsequent hot extrusion. The TEM results indicate that a nano-AlN particles transition layer is present on the surface of the Si3N4 particles, which has a good interfacial bonding with the Al matrix. The EBSD results show that the grains are refined significantly and the <111>Al fiber texture is improved in the Si3N4/2026 Al composite. At room temperature, the yield strength, ultimate tensile strength and Brinell hardness of composite are 454 MPa, 586 MPa and 143.5 HBW, respectively, which are increased by 15%, 12% and 11% than those of matrix alloy. The enhanced mechanical properties of the composite can be attributed to the load-bearing effect of the Si3N4 particles, grain boundary strengthening, dislocation strengthening and Orowan strengthening. This work will provide a new idea for the development of low cost and high strength Al matrix composites.