Microstructure and corrosion behavior of as-cast and heat-treated Al-4.5 Wt pct Cu-2.0 wt pct Mn alloys
- PDF / 6,811,803 Bytes
- 18 Pages / 612 x 792 pts (letter) Page_size
- 26 Downloads / 280 Views
I.
INTRODUCTION
A L T H O U G H it is generally agreed that aluminum alloys exhibit good corrosion resistance to marine environments, many are susceptible to localized corrosion. Previous work on copper-bearing aluminum alloys showed intergranular corrosion to be associated with (1) the presence of a solute-depleted region and (2) an alloy rest potential intermediate between the pitting potentials of the intergranular region and the a matrix. I~.2,31 Copper dissolving from such an alloy may be reduced by aluminum and precipitate in metallic form to create a detrimental galvanic couple with a potential difference of about 1 V. Addition of manganese to aluminum alloys has little or no effect on corrosion, since AI6Mn, which is usually present, has a corrosion potential similar to that of aluminum, t21 Also, if iron and iron-silicon compounds are present, as in commercial AI-Mn alloys, manganese tends to combine with them to form (Fe, Mn)AI6 or (Fe, Mn)3Si~AIIs, which also have corrosion potentials similar to that of aluminum, 14j and the corrosion resistance is improved. Results of the effect of manganese in solid solution on corrosion potentials are contradictory. It has been reported that manganese has no effect lsl and also that it shifts the corrosion potential toward more cathodic v a l u e s . 16"7"81 In the semiwrought AI-5 wt pct Cu alloy, Paganelli tgl concluded that extended artificial aging can improve the resistance to intergranular corrosion and pitting. According to Galvele and De Micheli, m in aged AI-Cu alloys, a copper-depleted zone, which is anodic with respect to A12Cu and the grain body, is produced at the grain boundaries where A12Cu precipitates. Hence, the alloy is susceptible to intergranular corrosion. Addition of manganese reduces, to some extent, the susceptibility of
S.M. SKOLIANOS, formerly Graduate Student, Department of Metallurgy, University of Connecticut, is now Lecturer, Aristotelian University of Thessaloniki, Thessaloniki. Greece. T.Z. KAq"I'AMIS and O.F. DEVEREUX, Professors, are with the Department of Metallurgy, University of Connecticut, Storrs, CT 06268. Manuscript submitted March 16, 1988. METALLURGICAL TRANSACTIONS A
aged aluminum-copper alloys to intergranular corrosion, possibly because it tends to prevent the formation of Guinier-Preston zones in the matrix and, consequently, the microstructure, which is susceptible to intergranular corrosion.l~~ The effect of cooling rate during solidification on the corrosion of as-cast or heat-treated aluminum alloys is not very well established. Murty et al. fl~l have studied the corrosion characteristics of as-cast and heat-treated A1-4.5 pct Cu alloy in air-saturated aqueous 3.5 pct NaCI solution as a function of distance from the chill, hence, cooling rate, for conventional rates. It was concluded that the severity of corrosion in the as-cast condition increases with increasing cooling rate. It was also concluded that the intergranular attack and pitting in solutionized and aged material were similar to those occurring in corr
Data Loading...
