Something told me this would result in a debate!
Of the two elements, it is true that aluminium is more abundant in the earth�s crust than titanium. Titanium is third in line behind iron and aluminium in the most common metals list. Both pure titanium and pure aluminium are protected by a thin layer of metallic oxide that forms virtually instantaneously upon contact with the oxygen in air, and it is this layer which is responsible for their resistance to corrosion.
However, aluminium is far from being the ideal corrosion resistant metal and titanium surpasses it in many qualities.
Aluminium in the form of the pure metal is unable to withstand sustained atmospheric pollution and �acid rain�. The pure metal pits and eventually corrodes when used in exterior architectural structures. Atmospheric pollutants such as dilute sulphuric and hydrochloric acids attack it, although it is virtually inert to nitric acid at all concentrations. Consequently, pure aluminium used in exterior structures has a limited lifespan.
Solutions of alkalies such as sodium hydroxide (caustic soda) and potassium hydroxide rapidly attack aluminium in all but the lowest concentrations (< 0.001%)
Pure aluminium readily corrodes in marine environments, with seawater causing considerable corrosion in very short time. It is not used in the petrochemical industry, again because contact with a large number of organic chemicals will corrode the metal.
You will note that these environmental conditions are far from being out of the ordinary and aluminium corrosion is quite commonplace.
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