Research On Mechanical Property And Corrosion Properties Of Rapidly Solidified 7075 Aluminum Alloy By Hot Extrusion

Aluminum and aluminum alloys are the second largest group of metals with the most extensive use and wide applied ranges besides iron and steel,its output ranks first among non-ferrous alloys.Among which 7075 aluminum alloy is the most common type with high strength,low density but poor corrosion resistance.It's widely used in fields such as aerospace,architecture and military,etc.While 7075 is used,especially when it comes to coastal environment where corrosion is more likely to happen,the study of 7075 aluminum alloy is mainly focused on how to improve the strength of the material as well as its ability to resist corrosion.In this research,7075 aluminum alloy was processed by undertaking single roll melt rotating cooling method to rapid cooling to obtain fine crystal 7075 aluminum alloy ribbon,which was immediately shaped to aluminum alloy bars by hot extrusion.The microstructure,mechanical properties and corrosion resistance of rapid solidification aluminum alloy ribbon,melt spinning hot extrusion aluminum bar and cast hot extruded aluminum alloy bar were analyzed respectively by DSC,SEM,XRD,EBSD,hardness test and tensile test,etc.The heat treatment process was studied and the critical conclusions were as follows:?1?Fine crystal alloy ribbon was generalized after performing rapid solidification on7057 aluminum alloy in vacuum ambiance,and the obtained aluminum alloys were greatly refined compared to cast aluminum alloy.Grains on the side of the copper wheel were fine and uniformed whereas the ones away from the wheel were rough and uneven.The cooling rate was accelerated during the rapid solidification,hence increasing the solubility of alloying elements in aluminum matrix.The lattice constant was 4.05406?,which was higher than cast aluminum alloy.The rapid solidification process also caused lattice distortion of aluminum alloy and made the alloy grain become fine and even.The rapid solidification process was unequilibrium,and in accordance to the EBSD diagram,the rapid solidification process reoriented the grains,which were with preferred orientation of 7075 cast aluminum alloy,to the state of disordered orientation distribution.The grains of 7075 aluminum alloy were fine and even with an average size of 4.4?m.?2?Fine crystal 7075 aluminum alloy ribbon could be applied to structural parts by hot extrusion.With the temperature rising during the hot extrusion,the microstructure of alloy bar was densified gradually.Although grains coarsened,its strength and plasticity improved.Under the condition where extrusion ratio was 16 and temperature was 500?,optimal mechanical properties of hot extrusion bars were achieved.In this optimal situation,the tensile strength was 517.1 MPa and elongation was 8.8%.Comparing with cast hot extrusion,the grains of cast aluminum alloy after hot extrusion was refined dramatically and with a higher ability to grow.After the hot extrusion process,the non-preferred aluminum alloy thin ribbons formed a strong<111>silk texture along the extrusion direction,and a small amount of<001>silk texture.The silk texture made a positive contribution to the strength of aluminum alloy.?3?In the condition where the extrusion ratio was 16 and temperature was 500?,the optimum heat treatment process for the hot extruded aluminum alloy bar was solid solution480?×0.5 h+aging hardening 120?×24 h.The hardness of the aluminum alloy sample was 194.89 HV,tensile strength was 653.3 MPa and elongation was 6.3%.Its self-corrosion potential E_corrorr was-0.733 V and self-corrosion current density I_corrorr was 6.17?A/cm^2.Melt spinning aluminum alloy acquired greater strength and displayed better corrosion resistance ability than casting aluminum alloy under this heat treatment.