A 14-karat gold ring contains other metals that make it stronger than pure gold. What is this type of mixture called?
A mixture of 2 or more metals in various proportions is called an ALLOY.
Most of the metals we use are alloys. The utility of alloys have been appreciated since humanity began using metals for tools. For instance, tin and copper, as the (reasonably) pure elements, are soft and do not tend to keep an edge. Make an alloy of tin and copper (approx 10-15% tin) , and you get bronze, an alloy with excellent hardness and tool-making properties.
Mix quantities of iron and carbon and other metals and you get an even better tool making alloy; stainless steel is a modern example. All of this is the province of the metallurgist; we must have had some good ones in our technological history.