Microstructural effects on the spall properties of ECAE-processed AZ31B magnesium alloy

• Spall behavior of ECAE-processed AZ31B-4E Mg alloy was investigated.
• ECAE-process introduced fragmented intermetallic inclusions.
• Intermetallic inclusions were found to be responsible for the initiation of spall.
• Early stage of the spallation was dominated by nanovoid formation.

Time-resolved normal plate impact experiments and spall recovery experiments were conducted to study the spall behavior of AZ31B-4E magnesium alloy processed via Equal-Channel Angular Extrusion (ECAE). The spall strength and incipient spall damage in the specimens were measured at different shock stresses using 51 mm and 105 mm bore gas guns. The Hugoniot Elastic Limit (HEL) was measured to be approximately 181 ± 3 MPa. The spall strengths extracted from the free surface velocity profiles of the shocked specimens were found to decrease by 5% for shock stresses ranging from 1.7 GPa to 4.6 GPa. However, this reduction in spall strength may fall within the experimental error. Post-test fractographic examinations of recovered specimens revealed that spall failure originated at micrometer-size intermetallic inclusions and propagated through the material by cavitation events with a very limited growth of voids. It was concluded that the strengthening of AZ31B-4E magnesium alloy by the ECAE-process resulted in adverse effects on its microstructure and spall behavior because of the process-induced cracking of intermetallic inclusions and their weak interface strengths.