Microstructure And Mechanical Properties Of Nano-SiC Reinforced Al 7075 Alloy Based Composite

Aluminium alloys are nowadays present in almost every field of industry,from food packaging to automotive and aerospace,thanks to their good mechanical properties,which are coupled to an uncommon low density.Amongst them,the aluminium 7075 alloy,which is mainly alloyed with zinc element,received recently a particular attention,as a result of its high strength similar to these of some steel alloys.This material meets the requirements for the creation of a Metal Matrix Composite,which is a new type of composite that combines a metallic matrix with reinforcing particles,with the objective of enhancing the mechanical properties.In this study,a commercial powder of Al7075 alloy was submitted to a high energy ball milling with the addition of 5%wt.Silicon Carbide nanoparticles,in order to create a nano-SiC reinforced Al7075 alloy based composite.The powders were subsequently consolidated through two different processes,either Vacuum Hot Pressing or Spark Plasma Sintering.The consolidated powders were hot extruded at 460?C,while the effects of two different extrusion ratios,9:1 and 25:1 were tested.Finally,half the extruded rods underwent a T6 heat treatment.In total,six composite materials obtained through these different manufacturing processes were characterized with Vickers Hardness testing and tensile testing for the mechanical properties,and with X-Ray Diffraction and SEM for the microstructure.The obtained composites presented the characteristics of very strong and brittle materials,as a tensile strength between 580 and 650 MPa was found,alongside an elongation to fracture between 1 and 1.5%.Results proved that the choice of the sintering method has an influence on the mechanical properties,as better powder consolidation quality was achieved by SPS rather than VHP,which contributed to the good mechanical properties of the as-extruded material.Increasing extrusion from 9:1 to 25:1 has been found to cause the as-extruded materials to be more sensitive to the impurities during tensile deformation,which induces the occurrence of immature fracture and consequently the decrease of mechanical strengths.The SEM observation and the results of the tensile tests highlighted that cracks are easily formed in the as-extruded materials during heat treatment,due to the presence of high internal stresses,which cause lower mechanical properties of the T6 treated samples.However,in some cases,the T6 heat treatment was noticed to lead to an improvement of the mechanical properties and especially of the ductility.The purpose of this thesis is to investigate the microstructure and the mechanical properties of the Nano-Sic reinforced Al Matrix Composites and to discuss the influence of the manufacturing parameters on the microstructure and the mechanical properties.