0.2197 m c a m a c a m c c m     + +   =     +     ( /( )) m c m m + ( / / ) ( / / ) a c a m a c a m + = + World Engineering & Applied Sciences Journal 11 (1): 06-12, 2020 ISSN 2079-2204 © IDOSI Publications, 2020 DOI: 10.5829/idosi.weasj.2020.06.12 Corresponding Author: C.I. Nwoye, Chemical Systems and Data Research Laboratory, Department of Metallurgical and Materials Engineering, NnamdiAzikiwe University, Awka, Nigeria. 6 Response of Heat Affected Zone Hardness of Air Cooled Aluminium, Cast Iron and Mild Steel Weldments to the Welding Voltage C.I. Nwoye, H.C. Otamiri, T.G. Okafor, M.K. Edojah and I.C.C. Iloabachie 1 2 3 4 5 Chemical Systems and Data Research Laboratory, Department of Metallurgical and 1 Materials Engineering, Nnamdi Azikiwe University, Awka, Nigeria Department of Mechanical Engineering Technology, 2 Akanu Ibiam Federal Polytechnic, Afikpo, Ebonyi, State, Nigeria Department of Mechanical Engineering Technology, 3 Federal Polytechnic, Oko, Anambra State, Nigeria Department of Mechanical Engineering, 4 Delta State Polytechnic, Otefe-Oghara, Delta State, Nigeria Department of Mechanical Engineering, 5 Institute of Management and Technology, Enugu, Enugu State, Nigeria Abstract: Response of heat affected zone hardness of air cooled aluminium, cast Iron and mild steel weldments to the welding voltage carried out. The materials were weldedusing the shielded metal arc technique and the HAZ hardness of their respective weldmentsevaluated following cooling in air. Three multi-factorial models were derived and used as empirical analytical tools for the predictive evaluation of the HAZ hardness resulting from mathematical input of welding voltage influence. The results of the evaluation indicate that the HAZ hardness of these weldments are significantly affected by the input welding voltage. On similarly cooling aluminium, cast iron and mild steel weldments in air followingwelding,the derivedmodel expressed as: evaluates aluminium weldment HAZ hardness by multiplying the computedgeneral voltage product rule (GVPR) (( + )/ ) with the ratio; HAZ hardness product of cast iron and mild steel/ HAZ hardness sum of a m a c c m 0.2197 cast iron and mild steel . Other derived models show that the weldment HAZ hardness of each of cast iron and mild steel relative to the others is significantly dependent on the GVPR which is a collective function of their respective welding voltages. The validity of the model was found to be rooted in the core model expression; where both sides of the expression are correspondingly equal.Comparative evaluationof results from experiment and derived model shows that aluminium weldment HAZ hardness per unit welding voltageare 1.3143 and 1.3142(VHN)V respectively. Similarly, cast iron 1 weldment HAZ hardness per unit welding voltage as evaluated from experiment and derived model are 3.7455 and 3.7463 (VHN) V respectively. Furthermore, mild steel weldment HAZ hardness per unit welding voltage 1 evaluated from experiment and derived model are 2.1409 and 2.1412 (VHN) V respectively. The maximum 1 deviation of model-predicted HAZ hardness from the experimental results is less than 0.03%, translating to over 99.97 % operation confidence level for the derived models. Key words: Response Heat affected zone hardness Air cooled aluminium Cast Iron and mild steel weldments Welding voltage