Metal-fusing alloy is a term used to describe an alloy that is used in the process of soldering. Soldering is a process in which two or more metal pieces are joined together by melting and flowing a filler metal into the joint. The filler metal has a lower melting point than the metals being joined, and it forms a strong bond when cooled. Metal-fusing alloys are commonly used in electronics, plumbing, and jewelry making.