Stress corrosion cracking resistance of aluminum alloy 7000 series after two-step aging

Abstract

The effect of one-step and a new (short) two-step aging process on the resistance to stress corrosion cracking of an aluminum alloy 7000 series was investigated, using slow strain rate test and fracture mechanics method. The aging level in the tested alloy was evaluated by means of scanning electron microscopy and measurements of electrical resistivity. It was shown that the alloy after the new two-step aging is significantly more resistant to stress corrosion cracking. Values of tensile properties and fracture toughness are similar for both thermal states. Processes that take place at the crack tip have been considered. The effect of the testing solution temperature on the crack growth rate on the plateau was determined. Two values of the apparent activation energy were obtained. These values correspond to different processes that control crack growth rate on the plateau at higher and lower temperatures.

Ispitivan je uticaj jednostepenog i novog (kratkotrajnog) dvostepenog termičkog taloženja na otpornost prema naponskoj koroziji aluminijumske legure serije 7000, primenom metode male brzine deformacije i metode mehanike loma. Stepen starenja ispitivane legure je procenjen primenom skening elektronske mikroskopije i na osnovu merenja električne otpornosti. Pokazano je da je legura posle novog dvostepenog termičkog starenja znatno otpornija prema naponskoj koroziji. Vrednosti zateznih karakteristika i žilavosti loma su slične za oba termička stanja legure. Razmatrani su procesi koji se odvijaju na vrhu naponsko-korozione prsline. Određen je uticaj temperature rastvora za ispitivanje na brzinu rasta prsline na platou. Određene su dve vrednosti prividne energije aktivacije. Ove vrednosti odgovaraju različitim procesima koji kontrolišu brzinu rasta prsline na platou, na visokim i niskim temperaturama.