EFFECT OF ETCHING PROCESS PARAMETERS ON STREAK DEFECT IN ANODIZED ALUMINUM

Abstract

A streak defect on anodized aluminum is a major problem in the aluminum extrusion industry. It causes uneven color (dull or bright) on the surface of the extruded parts and can be easily observed. Many factors can contribute to the streak defect, such as poor surface quality of the extrusion die, abrupt change of bearing on the extrusion die, etc. In the current practice, a trial and error method is used during the etching process to eliminate the streak defect and this approach increases the production cost and time. The aim of this study is to experimentally investigate the effect of etching process parameters, i.e., concentration of NaOH, etching temperature and etching time on response variables (i.e., material loss, surface gloss difference and final surface roughness) of etched aluminum parts. The experiment was conducted in a total of 20 runs designed using Central Composite Design (CCD). Response Surface Methodology (RSM) was used to model and analyze regression equations for the response variables with the etching process parameters as the controllable factors. Analysis of Variance (ANOVA) was used to investigate the significance of these parameters to determine the regression equations as the predictive models. For the model validation, the predicted results showed high accuracy with maximum errors of 0.55% and 18% in weight loss and difference in surface gloss, respectively. Additionally, contour and 3D surface plots were obtained from RSM and were used to discuss the main effects and the interaction effects of the process parameters. Moreover, the overlaid contour plots in CCD analysis were used to determine an operational range for the removal of streak defect on extruded aluminum. Based on these results, guidelines for suitable etching process parameters to eliminate the streak defect on aluminum extrusion parts are provided.