A method of joining an element of metal material to an element of plastic material , in particular plastic material reinforced with fibers, wherein one or more slots are provided in a portion of said element of plastic material , said method being characterized in that it further comprises the following steps: - for each slot of the element of plastic material , providing a corresponding tab in the element of metal material, said tab having a cross-section with shorter width (w) and length (I) than the width (W) and length (L) of the slot , - arranging the element of metal material and the element of plastic material in a position of mutual coupling wherein each tab of the element of metal material is inserted through a corresponding slot of the element of plastic material , each tab having an end portion (2B1) protruding beyond said portion of the element of plastic material , - performing laser welding by directing a laser beam (F) above the end portion (2B1) of each tab protruding beyond said portion of the element of plastic material , - directing a laser beam (F) above the end portion (2B1) of each tab that protrudes beyond said portion of the element of plastic material , so as to locally melt the metal material of each tab and create an enlarged head (2B2) on each tab, which is welded above said element of plastic material , so as to rigidly connect the element of metal material and the element of plastic material to each other, said method being further characterized in that one or more slots formed in the element of plastic material have an angled configuration, with two inclined sides, and the element of metal material has a corresponding tab with a corresponding shaped cross-section, or two separate tabs designed to engage the two different sides of the same angled slot. - for each slot of the element of plastic material , providing a corresponding tab in the element of metal material, said tab having a cross-section with shorter width (w) and length (I) than the width (W) and length (L) of the slot , - arranging the element of metal material and the element of plastic material in a position of mutual coupling wherein each tab of the element of metal material is inserted through a corresponding slot of the element of plastic material , each tab having an end portion (2B1) protruding beyond said portion of the element of plastic material , - performing laser welding by directing a laser beam (F) above the end portion (2B1) of each tab protruding beyond said portion of the element of plastic material , - directing a laser beam (F) above the end portion (2B1) of each tab that protrudes beyond said portion of the element of plastic material , so as to locally melt the metal material of each tab and create an enlarged head (2B2) on each tab, which is welded above said element of plastic material , so as to rigidly connect the element of metal material and the element of plastic material to each other, said method being further characterized in that one or more slots formed in the element of plastic material have an angled configuration, with two inclined sides, and the element of metal material has a corresponding tab with a corresponding shaped cross-section, or two separate tabs designed to engage the two different sides of the same angled slot. <EOS>