You can as Dave says update the part family members.
There are 2 ways :
1) Open the part family template ( the file that carries the Excel sheet.)
Assign the desired material to the solid-s in that file.
Tools - Part families, make sure that there is no column "material" in the lower list. If ithere is , delete that.
Open the Part family spreadsheet ( Excel)
select all rows, - Update members.
All members of this family will have the same material.
2) Open the part family template
Assign the desired material to the solid-s in that file.
Tools - Part families,
Add the column "material"
Open the Part family spreadsheet ( Excel)
you can now , per member, set a material . ( I think the name should match the name in the materials library to "Connect")
select all rows, - Update members.
This method allows you to have "the same fastener" in different materials. ( each member requires a unique line in the spreadsheet.)
Regards,
Tomas