partial melting; partial fusion
Technical term used in geology, materials science, and related fields to describe the process where only a portion of a solid material melts.
Magma is generated by partial melting of the mantle.
This alloy is joined using partial fusion.
溶融 means 'melting' or 'fusion' in general, while 部分溶融 specifically refers to partial melting.
部分溶解 is 'partial dissolution' (in a solvent), whereas 部分溶融 is 'partial melting' (by heat).
Compound of 部分 (ぶぶん, 'part' or 'partial') and 溶融 (ようゆう, 'melting' or 'fusion'). The exact historical derivation is uncertain, but the term is a straightforward technical compound.