On mechanism of in-situ microwave casting of aluminium alloy 7039 and cast microstructure

Abstract

The demand for processing of aluminum alloys is increasing owing to their extensive use in high specific strength products. Consequently, need for development of a faster and economic route to process such materials has been felt. In the present work, the mechanism of a new process, called ‘in-situ microwave casting’, is discussed vis-à-vis the cast microstructure. The AA 7039 alloy was cast in-situ using microwave energy at 2.45 GHz and 1400 W in ambient environment inside an industrial microwave applicator. Principles of microwave hybrid heating (MHH) were used to heat the charge. The mechanisms of heating and melting of the charge are discussed; significant heating phases of the alloy during irradiation are explained through time–temperature characteristic. The role of oxide layer at elevated temperature during irradiation is presented in the context of microwave absorption by the alloy. The developed casts were characterized in terms of identification of microstructures and metallurgical phases, pattern of microstructures across the cast section, porosity and micro indentation hardness. The results reveal a dense cast with porosity < 2%; phase analysis indicates presence of MgZn2, Al3Fe and Al8Fe2Si intermetallic phases. The micro indentation hardness of the in-situ microwave cast was 85.5 ± 26.5 HV.