A fastening structure for securing two disparate sections of an aluminum silicon alloy product. A precipitation hardenable austenitic stainless steel bolt engages each hole of a first and second aluminum silicon alloy product sections to fasten the sections together. The fastening structure is optimally utilized in a high temperature environment having thermal fluctuations. In such environments, the precipitation hardenable austenitic stainless steel bolt has less than 15% thermal relaxation after thermal fluctuations, and in some embodiments, less than 13% thermal relaxation after thermal fluctuations. The invention is of particular use for the fastening of an engine block crankcase utilized in a high temperature environment having thermal fluctuations where an engine block, a crankcase bedplate and a crankcase cover are formed from AA 362.0 alloy.