Usage patterns
〈人〉が部長になるfor someone to become a department head/club president
He will become the head of the sales department starting next month.
部長に就任するto take up the post of department head
She took up the position of head of the development department last year.
部長を務めるto serve as department head/club president
He served as captain of the soccer club for three years.
部長に任命されるto be appointed as department head
He was appointed as the new department head.