MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF A 2091 ALLI ALLOY .3. QUANTITATIVE-ANALYSIS OF PORTEVIN LE CHATELIER INSTABILITIES AND RELATION TO TOUGHNESS IN AL-LI, AL-CU-MG AND AL-LI-CU-MG (2091) ALLOYS

The microstructure and mechanical properties of a 2091 alloy are studied and compared to simpler Al-Li and Cu-Mg alloys. For ageing times between 6 and 24 h at 150-degrees-C, the 2091 alloy exhibits a toughness drop and a simultaneous change in PLC characteristics (as evidenced by a combination of local and total strain measurements), but no significant change in microstructure, except for the size of delta' precipitation. SEM in situ tests show that plastic instabilities are always related to extra damage. A quantitative model accounts for the toughness drop, based on plastic dissipation by PLC active bands.