Effects of Intermetallic Evolution by Electrically Assisted Rapid Heat Treatment on the Mechanical Performance and Formability of Aluminum Clad Steel

Abstract

Aluminum clad steel (ACS) sheets are heat treated by electrically assisted rapid heat treatment (subsecond duration) to balance their strength and ductility. The results of microstructural analysis show that the electric current results in the formation of different intermetallic compounds (IMCs) attributed to the rapid heating and the athermal effect of the electric current. The different IMCs affect the interfacial bonding strength and the mechanical properties of the ACS sheet. The tensile tests suggest that the yield strength of the ACS sheet gradually decreases, while the elongation gradually increases up to the current density of 170 A/mm2. In contrast, a higher current density of 190 A/mm2 dramatically increases the thickness of the IMC layer, resulting in premature fracture of the ACS sheet due to early interfacial debonding. The fracture mechanism is found to be a matrix-dominated fracture or interfacial IMC-dominated fracture depending on the applied current density. Moreover, the U-shape forming test confirms that the enhanced interfacial bonding strength and favorable formability of the ACS sheet can be achieved by repeatedly applying the electric pulses of 170 A/mm2 four times rather than using the single electric pulse of 190 A/mm2 due to the formation of a thick IMC layer under the high current density of 190 A/mm2. The present study proves that the electrically assisted rapid heat treatment is an efficient method to balance the strength and formability of the ACS sheet.