Microstructure And Properties Control Of Highstrength And High-Damping AlZnMgCuZr Alloy Prepared By Rapid Solidification

Rapid development of aerospace,national defense and new energy vehicle puts forward the high requirements for strength and damping capacity of aluminum alloys.However,traditional aluminum alloys are low damping materials,which are difficult to meet the needs of vibration and noise reduction.High-zinc Al-Zn alloys have excellent damping capacity,but the pieces produced by tradition casting show low mechanical properties caused by their coarse microstructures and serious component segregations.Melt spinning,being one of typical rapid solidification methods,has a very rapid cooling rate,which can effectively inhibit the compositional segregations and refine structures,and fabricate high-performance ribbons.As-spun ribbons combined with the subsequent extrusion can be used to produce the block material with fine-grained structures and uniform composition.Based on the abovementioned backgrounds,in this work,two novel high-zinc Al-Zn based alloys(Al-27.2Zn-1.5Mg-1.2Cu-0.08 Zr and Al-13.2Zn-2.5Mg-1.2Cu-0.2Zr)were prepared by a combination of melt spinning and hot extrusion.The microstructures,mechanical properties and damping capacities of these two alloys were systematically studied.The effects of extrusion parameters and subsequent heat treatment process on the microstructures and properties of the alloys were also investigated.The internal reasons for high-strength and high-damping capacity of the alloys were shown by microstructure analysis.Following results can be obtained:Firstly,melt spinning has been used to prepare the Al-27.2Zn-1.5Mg-1.2Cu-0.08 Zr ribbons with a gradient microstructure from free surface to Cu wheel side and 90～150 μm in thickness.Compared with the traditional gravity casted specimen,this alloy has a finer grain(with an average size of about 3.4μm),higher solute solubility and precipitate density,without notable compositional segregations and coarse second phases.Because of the synergistic effects of various strengthening mechanisms such as precipitation strengthening,grain refinement strengthening and solution strengthening,the as-spun alloy shows the higher hardness and strength as compared to the traditional metal mold casted one.Secondly,a novel Al-27.2Zn-1.5Mg-1.2Cu-0.08 Zr alloy is prepared by a combination of melt spinning and extrusion.Moreover,the effect of extrusion ratio on microstructures,mechanical properties and damping capacities of the alloy is systematically studied.The research shows that high-strength and high-damping aluminum alloy,with fine-grained structures and high-density η’/GP precipitates,can be prepared by this method.In the experimental range of this study,with the increase of extrusion ratio,the solute solubility increases,the volume fraction of η phase decreases,the η’ percentage of overall precipitates reduces,and finally the mechanical property and damping capacity both decrease.When the extrusion ratio is 14.8,the alloy has the most excellent mechanical properties(485 MPa tensile strength and 5.3 % elongation)and damping capacities(0.020 internal friction factor at room temperature).Thirdly,the effects of subsequent heat treatment processes(350～480 °C solution treatment and natural/artificial aging)on microstructures and properties have been studied.The result shows that the optimum solution temperature for the alloy is 400 °C,otherwise results in quench cracking and over-burn.The alloy with 400 °C solution and naturally peak-value aging has fine grains(average size ～3.1 μm),and the η’ phase percentage of overall precipitates reaches to about 50 %.The alloy exhibits a high mechanical property and an excellent damping capacity,i.e.521 MPa yield strength,545 MPa tensile strength,5.3 %elongation and 0.011 internal friction factor at room temperature.The peak-value hardness can be reached after artificial aging at 120 ℃/30 min,which means the alloy has the rapid artificial aging hardening characteristics.The peak artificial aging alloy,with high density η’phase,whose yield strength,tensile strength,elongation and room temperature internal friction factor are 515 MPa、548 MPa、2.5 % and 0.009,respectively.Finally,based on the above research results,the design and preparation process of a new high-strength and high-damping AlZnMgCuZr alloy were explored.The results show that the recrystallization behavior of the alloy and the density of nano precipitates can be controlled by reducing the content of Zn and increasing the content of Mg and Zr,and finally to prepare a novel bimodal-structure Al-13.2Zn-2.5Mg-1.2Cu-0.2Zr alloy with high-strength and high-damping capacity.The peak artificial ageing alloy exhibits a 702 MPa tensile strength and 9.1 % elongation,with a internal friction factor of 0.020 at room temperature.