Investigation Of Hot Work Process, Microstructure And Mechanical Properties Of Multi-layer Spray Deposition SiC_p/FVS0611 Composite Sheet

To improve the mechanical properties of Al-Fe-V-Si heat-resistant aluminium further, the introduction of SiC particles into the alloys as reinforcement not only increases Young's modulus, abradability, but also elevates ambient temperature strength and high temperature strength. In this thesis, densification processes of SiCP/FVS0611 were studied through comparing hot extrusion process and hot pressing process, and the result showed that aggregation of SiC particles on the face of the composite sheet could be solved properly with the method of uniaxial hot pressing and the state of fully dense could be reached after the process. Furthermore, the microstructure, fracture mechanism, mechanical properties, strengthening mechanism, heat resistant property and corrosion resistance of SiCP/FVS0611 were investigated in this paper. Through the succeeding hot rolling, the sheet of SiCP/FVS0611 exhibited good mechanical properties. The conclusions of the thesis were drawn as follows.1. In the perform as-hot extruded, SiC particles laminate vertical to extrusion direction and aggregate near sheet superficial coat, which resulted in the hierarchical classification between SiC particles and Al matrix was evident. Compared with the as-hot rolled billet, this phenomena did not appear in the perform as-hot pressed. Furthermore, SiC particles distribute uniformly. After the process of hot extruding and hot pressing, the relative density of SiCP/FVS0611 composite sheet reached 99.5% and 99.1% respectively, hence, the state of full dense was achieved.2. The density of SiCP/FVS0611 was increased more after rolling. During the rolling process, the density of as-hot extruded composite decreased firstly, then increased, but as for the as-hot pressed composite, the density rose firstly, then declined and increased finally. The as-rolled FVS0611 composite after hot extrusion remained the as-hot extruded microstructure and SiC particles laminated vertical to extrusion direction and aggregated near sheet superficial coat, which resulted in the hierarchical classification between SiC particles and Al matrix was evident. The distance of SiC particles gradually decreased in the as-rolled FVS0611 after hot pressing and SiC particles distributed uniformly more.3. The microstructure of as-rolled SiCP/FVS0611 composites was consistedα-Al,α-Al12 (Fe,V)3Si andβ-SiC, whose size were 600-800nm, 50-100nm and 10μm, respectively. Thereinto, the volume fraction ofα-Al12 (Fe,V)3Si andβ-SiC were more than 20% and15%. Furthermore, disperse, fine and spherical Al12(Fe,V)3Si mainly located on the grain boundaries and few was situated in the Al grains. The tensile strength of SiCP/FVS0611 composite sheet fell gradually as the temperature rose.Under ambient temperature, the tensile strength was 420MPa, when temperature rose to 315℃and 400℃, the tensile strength was still up to 230MPa and 141MPa. Otherwise the room temperature tensile strength and elevated temperature tensile strength of the composite after being exposed 200h at 550℃reached up to 402MPa and 212.2MPa. Meanwhile, the elongation of SiCP/FVS0611 composite sheet declined as temperature rose.4 For spray-deposited SiCP/FVS0611 composite, the combination of brittle fracture locally and ductile fracture as a whole was the main fracture form. The poor plasticity had nothing to do with the plasticity of Al matrix and should be attributed to the plastic deformation of matrix was hindered by the discontinuous SiC particles which resulted in the torn grain near the SiC particles.5 The hardness of SiCP/FVS0611 composite didn't decline evidently after being exposed 200h at 550℃, at the same time, the size of Al12(Fe,V)3Si grew up hardly, only reached to 100nm. While when exposure temperature rose to 640℃, the hardness fell quickly and Al12(Fe,V)3Si grew up rapidly to 300nm after 10h. During the condition, the decline rate of hardness was smaller compared with FVS0812 alloy unreinforced with SiC particle, which illustrated that the introduction of SiC particles increased the thermal stability of FVS0611 composite.6 The corrosion rate of SiC/Al-Fe-V-Si composite augmented as the content of Fe increased. For instance, the corrosion rate of SiCP/FVS0611 was lower than that of SiCP/FVS0812. In addition, the introduction of SiC into the Al-Fe-V-Si alloy increased the corrosion resistance of the alloy.