Abstract
The main objective of this research was a study the simultaneous influence of cold working and particle reinforcement on mechanical properties of Al. The model composites were fabricated by cold pressing RAl1 aluminium and 5% and 10% SiC powders and hot extrusion with ratio 3.8 in isothermal conditions at 480°C with 90° die angle to 18 mm diameter. Some specimens were then cold drawn with linear velocity 1 m/min to 16% area reduction, and one specimen in 3 passes to 51% reduction in area. Mechanical properties of the near fully dense composites were determined by axial compression, bend tests and hardness measurement and their microstructures examined, showing near homogenous distribution of SiC particles in the aluminium matrix. The increase in Young’s modulus was from 67 to 74 GPa and to 82 GPa for 5% and 10% reinforcement, respectively. Drawing increased average yield strength from 70 to 100 MPa for Al, and from 74 to 110 MPa and from 80 to 115 MPa, for 5 and 10% reinforcement, respectively. The results indicate that there is a significant increase in E, in accord with the law of mixtures, through incorporation of SiC and a synergistic effect of SiC and plastic deformation during drawing on strength. An attempt is made to identify the various contributions to overall strengthening of Al by considering also Al-8.8Cu-6.3%Si-0.7Mg alloy. It appears that alloying and age-hardening have the greatest effect, but that contributions from hot, warm and cold working are not insignificant. As powder metallurgy processing is an important fabrication method, their incorporation into the processing schedule merits consideration.
Highlights
Silicon carbide particulate reinforcement of aluminium and its alloys is used generally to increase Young’s modulus and wear resistance
To obtain more precise input for the individual compositional and microstructural contributions to the overall strength, it is reported about the influence of a further postextrusion operation, cold drawing, using model systems for Al-5 and 10% SiC particles
The preforms were heated at 480°C before hot extrusion, with the extrusion ratio 3.8 to a diameter 18 mm
Summary
Silicon carbide particulate reinforcement of aluminium and its alloys is used generally to increase Young’s modulus and wear resistance. Strengthening in hot and warm forged and extruded composites has received special attention [7,8,10]. Closed-die forged Al-5%SiC and hot extruded Al-8.8Cu-6.3%Si-0.7Mg alloy were investigated. To obtain more precise input for the individual compositional and microstructural contributions to the overall strength, it is reported about the influence of a further postextrusion operation, cold drawing, using model systems for Al-5 and 10% SiC particles. Preforms were cold unilaterally pressed on a hydraulic press ZD100, at ambient temperature under 80 MPa with die diameter 35.3 mm. Some specimens were turned to 17.5 mm diameter before drawing. The microstructure and properties by means of hardness, compression and bend tests were examined of extruded and drawn materials
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