An Alloy is known as a mixture of chemical elements of which at least one must be a metal.
The chemical compounds with metallic bases are unable to retain all the properties of metal, whereas an alloy will retain all the properties of metal in the resulting material.
D-block elements forming alloys:
The atomic sizes of transition metals are relatively very similar to each other, which attributes to their nature of forming the alloys.
Due to this reason, the similar-sized metal can replace the other metal from its lattice and form a solid solution which is the alloy.
This also explains, why transition metals form homogeneous mixtures with one another or metals with non-metals in the molten state, which is also known as an alloy.
Hence, the reason why the d-block elements form alloys has been explained above.