Effect Of Squeezing Melt Temperature And High Pressure On Microstructures And Mechanical Properties Of Al-Cu Alloys

The Al-Cu alloy with high strength,excellent heat-resistance property,good forming property,has been widely applied in the field of aerospace,transportation.However,due to the wide crystallization temperature range of Al-Cu alloys,castings have lots of defects under gravity casting condition.Squeeze casting is an advanced and efficient near-net-shape forming technology that combines the characteristics of casting and forging,obtaining components with fine grains,high density and high mechanical properties.The squeezing melt temperature and pressure are key process parameters in squeeze casting.Researchers usually tend to focus on the pouring temperature.There is little concern about the melt squeezing temperature.There are many researches on applied pressure at present,especially below 100 MPa.Howeveer,thers are few researches on applied pressure which is above 100MPa.In fact,these two parameters have important effect on squeeze casting produce,and it is necessary to carry out targeted research.In this paper,Al-5.0Cu-0.6Mn alloys with different Fe content are studied,based on gravity casting and squeeze casting process,using optical microscope?OM?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,electron probe micro-analyzer?EPMA?,differential scanning calorimeter?DSC?,micro-hardness tester,universal tensile tester and other testing methods to study the effect of squeezing melt temperature on microstructures and mechanical properties.The effect of squeezing melt temperature and pressure on bi-modal structures in squeeze casting alloys are also studied.The effect of conventional pressure and high pressure on microstructures and mechanical properties of Al-5.0Cu-0.6Mn alloys with different Fe content are importantly analyzed.Main conclusions are as follows:?1?Al-5.0Cu-0.6Mn-0.5Fe-0.1Ti-0.1RE alloy is squeezed at different temperature in solid-liquid interval.When the squeezing melt temperature is increased from 590?to 650?,the ratio of liquid continuously increases,the secondary dendrite arm spacing,the volume fraction of second phases and shrinkage porosity are gradually reduced.However,the volume fraction of fine grains in bi-modal structures increases.The tensile mechanical properties of as-cast and T5-treated alloys increases slightly with the increase of the squeezing melt temperature.?2?There is a bi-modal structure phenomenon in the microstructure of as-cast alloy,in which fine grains are below 100?m and coarse grains are above 300?m.As the squeezing melt temperature gradually increases,the volume of fine grains in bi-modal structures gradually increases,and the difference of Cu concentration of grains also increased,and the segregation of the alloy composition deteriorates.As the pressure gradually increased,the volume of fine grains in bi-modal structures increases,and the uniformity of the alloy composition gradually decreases.?3?As applied pressure increased from 0 MPa to 100 MPa,secondary dendrite arm spacing,grain size,the volume of porosity and second phases,the size of second phases are significantly reduced.However,as applied pressure increased from 100 MPa to 500 MPa,secondary dendrite arm spacing,grain size,the volume of second phases and the volume of porosity are slightly reduced,but the size of second phases is still significantly reduced.?4?The high pressure has significant effect on the morphology of the second phases in alloys with different Fe content:In the as-cast alloy of 0 Fe,the second phase is??Al₂Cu?.In the alloy of gravity casting,??Al₂Cu?phases are coarse mesh shape with sharp ends.As the applied pressure gradually increases to 500 MPa,??Al₂Cu?phases are substantially rounded.In the as-cast alloy of 0.5 Fe,the Fe-rich phases changes from multi-branched Chinese script to small and short-branched when the applied pressure increases from 100 MPa to 500 MPa.In the as-cast alloy of 1.5 Fe,most of the needle like Al₆?FeMn?phases are transformed into the Chinese script Al₆?FeMn?phases with the increase of applied pressure.?5?The mechanical properties of as-cast and T5-treatred Al-5.0Cu-0.6Mn-xFe alloys are increased with the increased of applied pressure.However,the increase is obvious in the stage of 0¹00 MPa,and the increase is not obvious in the stage of 100⁵00 MPa.The elongation of the alloy under high pressure is more obvious than the increase of strength.With the increase of Fe content,the growth trend is more obvious.