Friction stir alloying of AZ61 magnesium alloy and SPHC mild steel with ZN-CNT additive / Muhammad Zulhiqmi Mohd Jamil

Muhammad Zulhiqmi , Mohd Jamil (2024) Friction stir alloying of AZ61 magnesium alloy and SPHC mild steel with ZN-CNT additive / Muhammad Zulhiqmi Mohd Jamil. Masters thesis, Universiti Malaya.

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Abstract

Joining dissimilar materials is one of the effective techniques and solutions for materials enhancement in strength and durability that could give more design flexibility. Different materials are joined together to produce a new lightweight combination that can be applied in various manufacturing and production related to aerospace, automotive, shipping and other industries. Magnesium alloy and mild steel were selected as the combinations as both materials have advantageous material characteristics and properties. Magnesium is lightweight and has vast applications used in the industry, meanwhile, mild steel has good strength and durability. The critical challenges in joining both materials are their vast differences in physical, mechanical, and chemical properties. The immiscibility of the two materials presents a challenge in their joining process. In this study, 1.5 mm of dissimilar AZ61 and SPHC mild Steel were welded in the butt joint configuration with different percentages of zinc-carbon nanotube powder added as an additive to promote and enhance the strength of the joint. Zinc is soluble with both Mg and Fe. Based on the phase diagrams of Zn–Mg and Zn–Fe, it shows well interactions between the elements. The joint was evaluated in terms of tensile strength, microhardness, and microstructural observation through Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and Transmission Electron Microscopy (TEM). Tensile test & microhardness results showed a significant enhancement of 125% and 495 HV for samples with 1 % CNT-Zn (balance) additive, respectively. Microstructural analysis revealed that the CNT was well dispersed in the joint interface at 15 mm/min welding speed. The addition of CNT, coupled with the intermetallic compound detected, is assumed to have contributed to the joining strength.

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