Porous anodic film formation on Al–Ti alloys in sulphuric acid

Anodizing of Al–Ti alloys, containing 3, 12, 15, 30 and 45 at.%Ti, is examined at 5 mA cm−2 in 1 mol dm−3 sulphuric acid at 293 K. Porous films are formed up to 15 at.%Ti, with titanium increasing the anodizing voltage and pore size. In contrast, a barrier-type film is formed at 30 at.%Ti, with a finely porous outer region, while at 45 at.%Ti, barrier-type film growth is accompanied by oxygen generation. Ti:Al atomic ratios in the films are similar to those in the respective alloys. Reduced levels of sulphur occur in barrier-type films compared with porous films.

► Porous anodic films are formed on Al–Ti alloys in sulphuric acid up to ∼20 at.%Ti.
► Atomic ratios of Al to Ti are similar in films and alloys.
► Incorporation of Ti4+ ions into anodic alumina increases the pore size.
► Films formed on Al–30 at.%Ti and Al–45 at.%Ti are largely barrier-type.
► Barrier-type films contain significantly less sulphur than the porous films.