<p>This study investigates the effect of thermal/straining conditions on the hardness distribution in tungsten-inert-gas welded AA5754 aluminium-alloy 4–6–8&#xa0;mm plates using alternating/direct current, with a focus on the influence of welding quality on deformation behavior and microhardness variation, its qualitative and quantitative analysis. Two hypotheses regarding effect of welding current on hardness were tested experimentally based on empirical equations. Tensile and hardness tests were employed to evaluate the mechanical properties and performance. The results revealed that hardness distribution in DC-samples is more stable with values ranging from 75 to 90 HV as the distance from the weld center increases. In contrast, AC-samples exhibited a wavier hardness profile (90 ÷ 95HV) before gradually reaching the base-metal hardness (60 ÷ 80 HV). AC-samples consistently demonstrated higher hardness (10 ÷ 15ΔHV) than DC-samples. However, as the plate thickness decreases, the difference in hardness between AC and DC samples diminishes (0ΔHV), suggesting that the thinner plates promote faster cooling, minimizing the thermal effects associated with current type. The study also highlighted the influence of strain hardening, which increased the overall hardness (up to 125 HV) and reduced fluctuations in hardness distribution. The distance at which the hardness stabilizes was found to be directly proportional to plate thickness and significantly effects the size of heat-affected-zone. Early strain hardening was observed in samples that break prematurely compared to the statistical average. Despite the differences in hardness distribution, the current type did not significantly affect the fracture toughness. The findings provide new insights into the relationship between current type, plate thickness and the mechanical behaviour in TIG-welded aluminium alloys.</p>