A heat-curable structural adhesive includes at least one non-rubber-modified epoxy resin; an optional rubber or toughener, one or more epoxy curing agents, one or more epoxy curing catalysts; and a flame retardant mixture that includes (i) alumina trihydrate, (ii) zinc borate and (iii) melamine or a melamine derivative. The structural adhesive is useful for bonding metals to other materials or metals to other metals. The structural adhesive strongly resists ignition when welding is performed in the presence of the uncured material, and does not interfere significantly with weld performance.