Corrosion of aluminium alloys in high temperature water — a survey

Abstract

In high temperature water aluminium alloys can be attacked in three ways: by grain boundary attack, by accelerated attack and by uniform attack. The grain boundary attack can be prevented by alloying with elements which form phases which are cathodic to aluminium. The beneficial influence is attributed to the exchange currents set up between the aluminium matrix and the phases of alloying elements. The accelerated attack can be controlled by proper fabrication technique and well-balanced additions of alloying constituents, and thus the main corrosion problem is the high uniform corrosion rate. It is proposed that the rate-controlling step in a dynamic system is the dissolution of aluminium oxide, and it is therefore difficult to propose alloys which have a lower corrosion rate than the best present ones. At 230° C in flowing water a corrosion rate of 0.1 mm/year is observed. This is increased to about 0.3 mm/year under boiling at 70 watt/cm 2. With proper design, aluminium-clad fuel elements might work satisfactorily at this temperature and perhaps even somewhat higher. A short comment is made on the mechanical properties of the corrosion resistant alloys and on the welding of these.