With the aim to improve mechanical properties of the layer formed by anodic oxidation of Al on the material EN-AW-1050-H24 the microhardness of the layer was investigated as a function of physical and chemical factors acting in the anodic oxidation at constant current density JA = 1 A dm-2. The electrolyte was a mixture of H2SO4 and oxalic acid. Emphasis was put on the effect of H2SO4 concentration ranging from 0.09 to 2.76 mol dm-3 on the microhardness. In the experiment were carried out 44 separate attempts with the change of the current values of the individual factors under defined levels for each implementation. With this in mind, the surface treatment processes are multifactorial systems where, except the main effects, reciprocal interactions are also very significantly influenced. Failure to respect these mutual relations of the operating agents, often leads to misconceptions and misinterpretations. Therefore, the paper also addresses the interaction of the chemical composition of the electrolyte with physical factors: time of anodizing, voltage and temperature of the electrolyte.