Mechanization refers to the replacement of human power with mechanical power of some form. The use of hand power tools is not an example of mechanization.
Automation and mechanization are often confused with each other; Mechanization saves the use of human muscles whereas automation saves the use of human judgement.
Mechanization displaces physical labor, whereas Automation displaces mental labor as well.
Mechanization affects one or two industries at a time. Automation is the replacement of human thinking with computers and machines. Automation create jobs for skilled workers at the cost of unskilled and semi skilled workers. It affects many industries at the same time.