Development of Al-5Cu/B4C Composites with low Coefficient of Thermal Expansion Produced by Squeeze Casting Technique.
Al-Si alloys have key importance in automotive application due its excellent properties in castability, low Coefficient of Thermal Expansion (CTE) and low density. For achieving low CTE in Al-Si alloys, the percentage of Si should be more than 10% of Aluminum but high silicon content affect the mechanical properties on both room and elevated temperature.
The aim of this research is to provide an alternative material for piston application with excellent mechanical properties and low Coefficient of Thermal Expansion (CTE). Composite material is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. multifunctional properties can be achieved in a single composite material. In this paper, We will propose Al-Cu as matrix and B4C as reinforcement to produce a composite material for piston application and we will report the thermal expansion behavior of a set of Al matrix composites reinforced with B4C (micrometer-sized) particles. It will be demonstrated that the concentration of B4C particles and method of production has significant effects on the CTE. Such effects will be discussed in terms of the effect of reinforced on the microstructures and porosity of the composites.
Al-5%Cu as metal matrix and B4C (2%, 5% and 7%) as reinforcement were used to produce composite via stir casting and squeeze casting technique for the automotive piston applications. The mechanical properties were tested, microstructure were examined by using Scanning Electron Microscopy (SEM), XRD was used to identify the phases in composites and analyzed CTE by dilatometer 402C at 100°C and 200°C. SEM results showed the uniform distribution of B4C particles in the composite, XRD showed new peaks of Al3BC and AlB2 in squeezed cast samples. These new phases Al3BC and AlB2 were formed in the result of pressure during squeeze casting and these phases are good for lower CTE. The pressure in squeeze casting eliminated the porosity and accelerates the facial reaction between reinforced particle and matrix. Coefficient of Thermal Expansion decreased with increasing the percent of reinforcement and hardness also increased after ageing at 200˚C and 250˚C. Mechanical properties of both composites enhanced with increasing concentration of B4C and a little decrease in plasticity after compression test at room and high temperature. The composite material with low CTE and good mechanical properties can be achieved via Squeeze Casting.
Supervisors - Dr. A. V. Pozdniakov.