High performance cast aluminium alloys for automotive applications

Abstract

Al-Si alloy of grade A356 is widely used in several industries such as automobile, aerospace , defence and others due to its lighter weight, high strength, excellent castability, excellent thermal conductivity, corrosion resistance, wear/abrasive resistance and other excellent mechanical properties. A356 alloy castings are used to manufacture aircraft parts, machine parts, truck chassis parts and structural parts which require high strength. Here we investigate the effect of squeeze casting and functioning of various master alloys, that are used to either grain refine the α-Al matrix or cause modification of Si morphology to improve the microstructural and wear properties like fretting wear and dry sliding wear of the Al-Si alloy. The most commercially used master alloys are Al-Ti-B alloy which act as a grain refiner and Al-Sr alloy which act as a modifier. To achieve better results, a combination of both grain refiner and modifiers is used to achieve fine α-Al phase and fine fibrous like Si particle morphology. However, as per previous research work it was investigated that the combination of AlTi-B alloy and Al-Sr alloy may cause a poisoning effect due to the reaction between Sr and B, which in turn reduces the modification ability of Sr. Hence in this research work, an attempt was made to find out an optimum amount of both of these master alloys that should be used to obtain better results in terms of microstructural refinement, modification of morphology of Si particles and other intermetallic phases and improvement in mechanical properties like hardness and wear properties. A combination of 750ppm of Ti and 150ppm of B added in the form of Al-5Ti-1B master alloy and about 200ppm of Sr added in the form of Al-10Sr master alloy to squeeze cast A356 alloy, showed significant improvement in hardness and wear properties of the alloy due to refinement of grain size and change in the morphology of Si and other iron based intermetallics.. Moreover, the process of squeeze casting under a pressure of 200MPa, also improved the wear properties of the alloy due to reduction in porosities, decrease in secondary dendrite arm spacings and modification of Si morphology. However, the combination of 750ppm of Ti, 150ppm of B added in the form of Al-5Ti-1B and 300ppm of Sr added in the form of Al-10Sr to squeeze cast A356 alloy, did not show much improvement in the wear properties of the alloy. Further investigation is required for more conclusive results.