Solderability
Some materials are easier to solder than others. Copper, silver, and gold are easy to solder. Iron and Nickel are a little more difficult. Titanium, magnesium, cast irons, steels, ceramics, and graphites are hard to solder. However, if they are first plated they are more easily soldered. An example of this is tin-plating, in which a steel is sheet coated with tin so that it can be soldered more easily.
Read more about this topic: Dip Soldering