Bond strength of a laser-clad iron-base alloy coating on Al–Si alloy substrate and its fracture behavior

An S250 MK3 type SEM equipped with a tensile stage was used to measure the bond strength of a laser-clad iron-base alloy coating on an Al–Si alloy substrate. Results showed that the bond strength chiefly depended on the substrate temperature and the Al content added into the cladding. At a low temperature range of 200–240°C, an increase of the substrate temperature resulted in a sharp reduction of cracks and thus a significant rise of the bond strength (from 17 to 104 MPa). At a range of 240–325°C, the bond strength was maintained at a higher level (about 90 to 110 MPa). When the substrate temperature was over 325°C, an unexpected reduction of bond strength was obtained because overmelting of the substrate caused a large dilution in the cladding and produced more low strength aluminides where the cracks initiated. Increasing the Al content from 0 to 3 wt.% in the cladding also reduced flaws or cracks in the transitional region and improved the bond strength. Dynamic observation of the fracture process showed that cracks initiated at the edge of the aluminum-rich area, where some low-strength aluminides (such as FeAl3 and Fe2Al5) existed, propagated to the intermediate area and slowed down in the iron-rich area. Fracture morphology analysis showed that the fracture was brittle.