PERFORMANCE EVALUATION OF Al-Mn ALLOY IN SEA WATER ENVIRONMENT AND PREDICTION OF EXPOSURE TIME BASED ON ITS CORROSION RATE AND INITIAL WEIGHT

Abstract

The performance of aluminium-manganese alloy in sea water environment has been evaluated by submerging the

alloy produced at varying Mn input range: 1- 4 wt % into a 99% purity aluminium powder. It was observed that

increased concentration of Mn in Al-Mn alloy (1-3%) resulted in increase in corrosion rate of the alloy (in presence

of sea water) due to the strong affinity between aluminium and oxygen which enabled oxygen to significantly

oxidize aluminium, forming oxide films. This implied that oxide film formation occurred simultaneously with

corrosion attack. A model was derived to predict the alloy exposure time based on its initial weight and corrosion

rate in the same environment. The validity of the derived model;

Txp = - 5638.5 ɤ 2 – 64.35 β2 + 125.29 ɤ + 2.9279 β – 0.653 was rooted on the core expression Txp + 0.653 = -

e1 ɤ 2 – e2 β 2 + e3 ɤ + e4 where both sides of the expression are correspondingly approximately equal. Comparative

statistical analysis of results from a standard model (regression model) derived model and experiment shows that

the standard error in predicting the alloy exposure time for each value of the initial weight and alloy corrosion rate

are 3.6752 x 10-5 & 0.017%, 0.0096 & 0.0217% and 0.0084 & 0.0203% respectively. Similarly, the F-test results are

2.47 x 10-5 & 0.3471, 2.29 x 10-5 & 0.3298 and 2.01 x 10-5 & 0.3024 respectively. Furthermore the correlation

between exposure time and corrosion rate & initial weight as obtained from experiment, derived model and

regression model were all > 0.97. Computational analysis of results generated from regression model, derived

model and experiment shows that the depths of corrosion penetrations are 9.5288 x 10-4 , 9.8728 x 10-4 and 9.89 x 10-4

mm respectively. Deviational analysis indicates that the maximum deviation of the model-predicted alloy exposure

time from the corresponding experimental value is less than 14.58%. This translated into over 85% operational

confidence for the derived model as well as over 0.85 reliability response coefficient for the dependence of the alloy

exposure time on corrosion rate and initial weight of alloy.