Effect of oversolidus barothermal treatment on the microstructure and properties of binary hypereutectic Al-Cu alloys

This study investigates the effect of oversolidus barothermal treatment (BTT) on microstructure and properties of binary alloys Al-22Cu and Al-27Cu ( at.%), focusing on the pressure-induced shifts in solidus and liquidus temperatures. The pressure shift of the solidus and liquidus temperatures was established at a hydrostatic argon pressure of similar to 100 MPa using the differential barothermal analysis (DBA). The solidus temperature of both alloys increased by approximately 8 degrees C during heating, aligning closely with the equilibrium state diagram upon cooling. The liquidus temperature of the alloys at 100 MPa increased by 11 degrees C for Al-22Cu and by 14 degrees C for Al-27Cu compared to the phase diagram. Taking these results into account, barothermal treatment of the alloys was carried out at 100 MPa and 570 degrees C for 240 min ( BTT1), as well as at 100 MPa and 562 degrees C for 10 min (BTT2). Processing of alloys at BTT1 leads to the primary Al2Cu particle size significant increase to lengths of 350-1500 mu m and widths of 150-400 mu m. During BTT1, the structure of the initial lamellar eutectic Al-Al2Cu is modified with the formation of discrete intermetallic particles, with the length and width being 15-240 and 1-3 mu m, respectively. With a decrease in temperature and exposure time, a significantly less intense increase in the size of primary intermetallic compounds occurs, and a noticeable increase in discrete eutectic intermetallic compounds occurs. The microhardness reached 2043 MPa for the eutectic (initial Al-22Cu). For the intermetallic and the eutectic, the microhardness was 4189 and 2699 MPa, respectively (initial Al- 27Cu); for intermetallic and the eutectic 4754 and 1382 MPa, respectively, for the Al-22Cu alloy processed at BTT1, and the eutectic microhardness for the Al-22Cu composition processed at BTT2 was 2409 MPa. The bending strength of alloys decreases after oversolidus BTT.