Effects of ageing time on the mechanical and conductivity properties for various round bar diameters of AA 2219 Al alloy

In the present study, AA 2219 alloys of 120 mm round bar are forged into various round bars (25, 50, 75 mm) and subjected to T6 temper heat treatment to identify the peak ageing time for various round bars. The electrical conductivity of the round bars is also measured and correlated with the mechanical properties. It is found that the peak ageing time is 23 h and does not vary up to 75 mm round bar. It increases to 25 h for the 120 mm round bar. The yield and tensile strength of the alloy are found to be in the range of 288-304 MPa and 410-428 MPa for the peak ageing condition. The hardness and conductivity vary in the range of 121-128 BHN and 30-30.96% IACS respectively for the peak ageing condition. Although a near linear relation is found to exist between the strength/hardness and the electrical conductivity values for the selected heat treatment parameters (solution temperature: 535 °C, ageing temperature: 191 °C and the peak ageing time: 23 h), the slope of the curve is different for different round bars. Microstructure characterization studies show the precipitate coarsening with increasing ageing time. Further, precipitate segregation is not found in the microstructure for any cases of round bar diameter and ageing time combinations.