Effect of Cerium and Isothermal Treatment on Mechanical Properties and Microstructural Evolution of Al-Si-Mg (A356) Alloy

Aluminium has been identified as one of the most used metal in engineering applications owing to some overwhelming properties possessed by the metal. Aluminium in its pure form does not have strong place in engineering application, but when alloyed with other metals and non-metals the properties improved tremendously to the expectation of engineering application. It is alloys have been developed using different elements, such as silicon, copper, magnesium, manganese, zinc, tin, etc, either singly or in combination. Among aluminium alloys, aluminium-silicon alloy are the most used aluminium alloy in various aspects of engineering application, due to its strength, wear resistance, corrosion resistance, castability, fluidity, etc. But, it is prone to brittleness owing to the development of coarse columnar grain structures of eutectic silicon, which reduces the ductility of the alloy. To take care of the formation of the eutectic silicon, certain elements are added in traces in order to change coarse structures formed by the eutectic silicon to fibrous or fine flake structures, which induces ductility back to the alloy. In this paper cerium (rare earth metal) was used as the chemical for modification of the eutectic silicon in the aluminium alloy. After the development of the A356 alloy cerium was added in varied percentages as 0.5; 1.0; 1.5; 2.0; 2.5%Ce. Heat treatment was done on one sample out of each pair of all the composition. Tensile test, Hardness test and microstructural examination (SEM) was carried out. The results show that cerium improved the ductility of the samples, such that there is proportionality in relation to mechanical properties. UTS is 411.78 vs 400.05MPa for 0% cerium heat treated and non-heat treated respectively, while the samples with the highest cerium contents (2.5%Ce) have UTS of 447.86 vs 442.62 for heat treated and non-heat treated respectively. Their hardness (HBN) are 307 (0%), 390 (1.0%) and 439 (2.5%) for heat treated. and 349 (0%), 391 (1.5%) and 459 (2.5%) for non-heat treated. The microstructure was modified with addition of cerium and is even better with heat treatment.