except that the anodic oxidation treatment was performed by using as an electrolyte an alkaline aqueous solution ph 13 7 in which 100 g l of sodium salicylate nac 7 h 5 o 3 and 20 g l of sodium hydroxide were dissolved under the conditions of a solution temperature of 15 u00b0 c an electrolysis voltage of 19 v and an electrical quantity of 40 c cm 2 the obtained aluminum alloy materials were each measured for the l value the results are shown in table 17 the results shown below confirmed that the l value was reduced highly blackened in the cases of hear treatment at from 100 u00b0 c to 400 u00b0 c as compared to the non treated case it was revealed that of those cases the l value was satisfactorily reduced in the cases of heat treatment at from 200 u00b0 c to 350 u00b0 c as compared to the non treated case the samples were revealed to be remarkably blackened particularly in the cases of 250 u00b0 c u00d7 120 minutes 300 u00b0 c u00d7 30 minutes to 120 minutes 350 u00b0 c u00d7 30 minutes to 120 minutes and 400 u00b0 c u00d7 30 minutes in addition for examining the precipitation state of mgzn 2 through annealing in the surface treated aluminum alloy material for experiment the integral diffraction intensity at the.