Daniel, Tilahun (PhD)Okelo, Fekadu2018-12-202023-11-182018-12-202023-11-182018-10http://etd.aau.edu.et/handle/12345678/15208Heat affected zone properties has been investigated in order to find changes in property of material due differences in welding parameters and conditions to achieve properties fulfilling the requirements put on welded structures. During welding, the high-temperature fusion process causes micro-structural and mechanical property changes adjacent to the weld line in the heat affected zone, which significantly alter the mechanical properties of the parent material. This work investigates mechanical properties and width of heat affected zone and microstructure of mild steel welded using manual metal arc welding process by preparing specimens with different thicknesses and welding parameters. Experiments carried out to understand the effect of heat input with focus on welding current and welding speed on hardness, tensile strength, toughness, width of heat affected zone and micro structure,. The results of the investigation indicate that significant increase in hardness with increase in heat input. Increase in welding speed which means decrease in heat input resulted in decrease in value of hardness of heat affected zone. From the experiment average HAZ hardness is higher than parent metal hardness by 16.5 % and HAZ toughness and tensile strength is lower than that of the parent material by 6.5% and 18.5% respectively. Varying the welding current found to cause more significant changes on mechanical properties of heat affected zone than varying welding speed. Thinner plates have wider heat affected zone compared to thicker plates for same heat input and with increase in heat input toughness and tensile strength decreased. Microstructure examination results show larger grain size in heat affected zone compared to the parent metal. Results from this work will be applicable in fabrication of low bed semi-trailer chassis components namely platte form and ramp. Moreover results from this work will be applicable in non-destructive testing of materials.en-USMicro structurefusionHeat Affected zoneManual metal arc WeldingParent MetalWelding parametersmild steelThesis