Reliability Level of Al-Mn Alloy Corrosion Rate Dependence on Its As-Cast Manganese Content and Pre-Installed Weight in Sea Water Environment

Abstract

The corrosion rate of Al-Mn alloy in sea water environment was studied, considering the catastrophic effect of salty water on aluminum alloy. The reliability level of the alloy corrosion rate dependence on its as-cast manganese content and pre-installed weight under service condition; in sea water environment was evaluation. Analysis of the surface structures of corroded Al-Mn alloys were carried out to evaluate the phase distribution morphology. The reliability response coefficient of the alloy corrosion rate to the combined influence of as-cast manganese content ϑ and pre-installed alloy weight ɤ were evaluated to ascertain the reliability of the highlighted dependence. Analysis of the surface structure of the corroded alloy revealed in all cases widely distributed oxide film of the alloy in whitish form. Increased oxidation of the as-cast Al-Mn matix (up to 3%Mn input) was due to increased permeability of the formed oxide film (to corrosive species in the sea water) as result of increased as-cast manganese content of the alloy (up to 3% Mn). Above 3% Mn input, the corrosion rate dropped indicating oxide film coherency and resistance to inflow of oxygen into the alloy. A two-factorial polynomial model was derived, validated and used for the predictive evaluation of the Al-Mn alloy corrosion rate. The validity of the model; was rooted on the core model expression ζ + ɤ2 - 0.002 ɤ - 0.2863 = - 0.0347 ϑ3 + 0.2431 ϑ 2 - 0.4848 ϑ where both sides of the expression are correspondingly approximately equal. The corrosion rate per unit as-cast manganese content as obtained from experiment and derived model were 0.0714 and 0.0714 mm/yr/ % respectively. Standard errors incurred in predicting the corrosion rate for each value of the as-cast manganese content & pre-installed alloy weight considered as obtained from experiment and derived model were 0.0333 and 0.03346 % & 0.0350 and 0.0363 % respectively. Deviational analysis indicates that the maximum deviation of model-predicted corrosion rate from the experimental results was less than 9%. This translated into over 91% operational confidence and response level for the derived model as well as over 0.91 reliability response coefficient of corrosion rate to the collective operational contributions of as-cast manganese content and pre-installed alloy weight in the sea environment.