With a simple iLogic macro you can check material assignment for each part saved from Inventor.
Creat a a new iLogic rule with the following contents:
materialName = ThisDoc.Document.ComponentDefinition.Material.Name
If materialName = "Generic" Then
objSPVoice = CreateObject("SAPI.SpVoice")
objSPVoice.speak ("Your component has no material assigned")
As a trigger for this rule, set e.g. "Before document save". A part with no material assigned will report itself automatically on save, by "telling it" (voice).
The default material for parts, or iLogic macros can be preset in the part template - see I > Save as > Save copy as template.