PURPOSE: To provide a cathode with which the inclusion of oxide inclusions and the formation of coarser crystal grains are prevented by deforming an Al-Si alloy contg. a specific ratio of Si after successively subjecting the alloy to homogenizing, cooling, spheroidization treating and cooling under specific conditions.

CONSTITUTION: The Al-Si alloy contg. 0.05 to 2% Si and desired additive elements is prepd. from 99.99% ultrapure Al, and a billet is manufactured therefrom. The billet is subjected to the homogenization treatment for ≥4 hours at 450 to 570°C, more preferably near 540°C and is then cooled by controlling the temp. down to the prescribed temp. of 330 to 450°C at a rate of 10 to 200°C/ hour to attain the Si precipitate concn. of 105 to 1010/cm2. The ingot is then subjected to the spheroidization treatment of Si by holding for ≥1 hours until the shape coefft. attains 0.1 to 1 and, thereafter, the billet is cooled by controlling the temp. down to room temp. at a rate of 5 to 100°C/hour to reduce the thickness of the product by the deformation and to uniformly increase the sizes in all the directions perpendicular to the thickness.