. " %, in particular 0.5 to 2 w. %, magnesium or containing 0.2 to 2 w. % manganese or containing 0.5 to 5 w. % magnesium and 0.2 to 2 w. % manganese, in particular e.g. 1 w. % magnesium and 0.5 w. % manganese, or containing 0.1 to 12 w. %, preferably 0.1 to 5 w. %, copper or containing 0.5 to 5 w. % zinc and 0.5 to 5 w. % magnesium or containing 0.5 to 5 w. % zinc, 0.5 to 5 w. % magnesium and 0.5 to" . . .