I tried to weld a copper wire on an aluminum plate, but I could not. How should I do this welding? Is there any substance I can pass on the aluminum for the solder to "get"?
Tin-lead solder does not really stick to aluminum. To make electrical connections to aluminum parts you must use insulated terminals. Drill a hole in the aluminum and with a screw secure the terminal. Then weld the wire in the terminal, as shown in figure 1.