Effect of equal channel angular pressing on microstructure and mechanical properties on non dendritic LM25 aluminium alloy

Mokhtar, Nurhasyinaz (2017) Effect of equal channel angular pressing on microstructure and mechanical properties on non dendritic LM25 aluminium alloy. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

This study is about the semisolid metal processing of aluminium LM25 alloy using cooling slope casting followed by equal channel angular pressing. In this experimental study, the most influential parameters between the pouring temperature and the length of cooling slope that affect the globalization of LM25 alloy during cooling slope casting were studied. Besides, the hardness, tensile strength and fracture behavior of cooling slope casting and conventional casting samples were investigated. All the experimental works were accomplished by using same LM25 aluminium alloy. The aluminium LM25 alloy feedstock billets were prepared through the cooling slope technique and conventional casting that were cast directly into mould. Several of samples were then treated with a T6 heat treatment that is solution treatment 520°C for 8 hours, quenching in water, followed by aging at 154°C for 4 hours. All of the samples were then observed by using optical microscopy (OM), Scanning Electron Microscope (SEM), hardness and tensile tests as well as fracture properties. The results revealed that at pouring temperature of 650°C and 400 mm cooling slope length, the LM25 alloy exhibits the spherical microstructural feature due to all dendritic structures were altered into ɑ-Al globule and rosette. The Vicker’s hardness value depicted that ECAP processed sample enhanced the highest hardness than conventional casting and cooling slope casting. In addition, it was observed that for ultimate tensile strength, the sample of ECAP with one pass only which is 188.98 MPa has the highest value compared to other conditions and as-cast sample. In all investigations and mechanical testing, the cooling slope casting that underwent T6 heat treatment revealed the obvious results which became the most dominant properties in microstructure distribution, hardness and tensile properties, in contrast with non-heat treated sample.

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