Microstructure And Properties Of Al-8Zn-2.5Cu-2Mg-xHo Alloy Under Different Heat Treatment Conditions

With the increasing use of ultra-high-strength aluminum alloys in automobiles,aerospace and other fields in recent years,as well as complex environmental changes during use,the performance requirements of ultra-high-strength aluminum alloys are also constantly increasing,both excellent mechanical properties,also requires good thermal conductivity.This experiment hopes to prepare a new ultra-high strength aluminum alloy with both thermal conductivity and mechanical properties to meet the development needs.In this experiment,the optical state?OM?,X-ray diffractometer?XRD?,scanning electron microscope?SEM?,energy spectrum analyzer?EDS?,universal experimental stretching machine,hardness tester and thermal conductivity meter were used to analyze microstructure,mechanical properties and thermal conductivity of the as-cast state Al-8Zn-2.5Cu-2Mg-xHo?x=0,0.1,0.3,0.5 wt.%?alloys and Al-8Zn-2.5Cu-2Mg-0.3Ho alloys under different heat treatment processes.The experimental results show:After adding the Ho element to the Al-8Zn-2.5Cu-2Mg alloy,the microstructure of the alloy changes from dendrites to equiaxed grains,and the Ho element can refine the grains.With the increase of Ho content,the grain structure of the alloy is more refined.When the Ho content is 0.5 wt.%,the grain size is the finest.The tensile strength,elongation and hardness of the alloy increase first and then decrease with the increase of Ho content.When the Ho content is 0.3 wt.%,the tensile strength,elongation and hardness of the alloy are the highest,respectively 175 MPa,7.5%and 127 HB.After the solution treatment of Al-8Zn-2.5Cu-2Mg-0.3Ho alloy at470?/40 min,the Mg Zn₂phase and Al₃Ho phase in the microstructure are most solid solution.At this time,the tensile strength and elongation of the alloy reach the maximum and the hardness is the smallest,320 MPa,13.219%and 111.5 HB,respectively.After the aging treatment at 150?/36 h,the Mg Zn₂phase and the Al₃Ho phase in the alloy structure are re-precipitated and disperse in the grain boundary and inside the grain.The tensile strength,elongation and hardness of the alloy reach the maximum,357 MPa,13.279%and 257.7 HB,respectively.The thermal conductivity of as-cast Al-8Zn-2.5Cu-2Mg-xHo alloy increases with the increase of Ho content at room temperature.When the Ho content is 0.5 wt.%,the thermal conductivity of the alloy reaches 108.452W/?m·k?and the thermal conductivity is best.With the increase of ambient temperature,the thermal conductivity of as-cast Al-8Zn-2.5Cu-2Mg-xHo alloy increases first and then decreases.When the ambient temperature reaches 210?,the Al-8Zn-2.5Cu-2Mg-xHo alloy with a Ho content of 0.3 wt.%has the highest thermal conductivity of 124.844 W/?m·k?.After the aging treatment of Al-8Zn-2.5Cu-2Mg-0.3Ho alloy,the thermal conductivity increase continuously with increasing aging temperature and aging time.When the aging system is170°C/24 h,the alloy has the highest thermal conductivity,reaching 169.495W/?m·k?,the best thermal conductivity.As the ambient temperature increases,the thermal conductivity of the alloy is also increasing.