Hot Pressing Sintering And Properties Control Of Aluminum-lithium Alloy For Drill Pipe

From 2020 to 2025,China has entered the era of deep oil and gas development.Aluminum alloy drill pipes are widely used in deep well drilling due to their low density,high specific strength,good corrosion resistance and non-magnetic properties.However,with the increase of drilling depth,aluminum alloy drill pipes face problems such as heavy weight and insufficient wear resistance.As the 21st century energy metal,Li has the characteristic of low density.Adding it to aluminum alloys can effectively reduce the density of the alloys.Based on the demand for light-weight,high-strength,and wear-resistant aluminum alloy drill pipes in deep well drilling,7075-Li alloys were prepared by hot pressing sintering by combining high-strength 7075 aluminum alloys with low-density Li alloys.The influences of hot pressing sintering process on the flow law and relative density of 7075 aluminum alloy powder were studied through numerical simulation,and the effects of Li on the microstructure,mechanical properties and tribological properties of sintered and solution-aged alloys were investigated.The main studies and results of this paper are as follows:（1）Based on the theory of continuum plasticity,the finite element model of material was established.The thermophysical parameters of 7075 aluminum alloy material were obtained by JMatpro software,and the process of hot pressing sintering of aluminum alloy powder was simulated using MSC.Marc finite element software.The influences of sintering process on the flow law and relative density distribution of powder were analyzed,and the simulated data of relative density of aluminum alloys was compared with the experimental data.The results show that the displacement of the powder gradually decreases along the pressing direction due to the pressure difference,and the displacement of the powder near the mold wall is smaller than that of the powder near the center of the compact in the same layer.As sintering temperature and pressure increase,so does the relative density of aluminum alloys and becomes stable gradually.A high relative density region is formed due to the maximum powder strain at both ends of the upper pressing head,while a lower relative density region is formed due to the lateral friction force and deformation extrusion of the middle particles adjacent to it,and a low relative density region is formed due to the minimum powder strain at both ends of the lower pressing head.The simulated values are in good agreement with the experimental values,and the range is determined for the sintering process of aluminum alloys containing Li.（2）7075-Li mixed powder with normal particle size distribution was obtained by ball milling process.Further optimize the sintering process with the target of increasing the relative density of the alloys.Under this sintering process,the effects of Li（0～2.0 wt.%）content on the microstructure and properties of sintered 7075 aluminum alloys were studied.The experimental results show that the relative density of the alloys increases and gradually stabilizes with the increase of sintering temperature and pressure.However,the relative density of the alloys decreases as the Li content increases,and the alloys have a high relative density（≥98.00%）under the process of 600℃and 60 k N.Aluminum alloys consist ofα-Al,η’（Mg Zn₂）,S’（Al₂Cu Mg）and Al_0.3Fe₃Si_0.7 phases.When Li is added,new S₁（Al₂Mg Li）phases appear.Newδ’（Al₃Li）andδ（Al Li）phases occur in the alloys as Li concentration is more than 1.5 wt.%.With the increase of Li content,the hardness and wear resistance of the alloys increase initially and then decrease gradually.When Li content is 0.25 wt.%,the highest hardness of the alloys is86.84 HV,and the lowest wear rate of the alloys is 2.21×10^-3 mm³·N^-1·m^-1.However,the tensile strength and elongation of 7075-Li alloys decrease gradually,transitioning from ductile fracture to brittle fracture.The alloys all experience oxidative wear.7075 aluminum alloys have adhesive wear,and Aluminum-Lithium alloys gradually change from abrasive wear to adhesive wear.（3）The heat treatment process of 7075-（0.25～2.0 wt.%）Li alloys was determined by thermal analysis and peak hardness of aged 7075 aluminum alloys.Under this process,the effects of Li content on the microstructure and properties of solution-aged 7075 aluminum alloys were investigated.According to the results,the solution and aging treatment of 7075-Li alloys is 500℃×2 h+120℃×24 h.Both S’（Al₂Cu Mg）and S₁（Al₂Mg Li）phases appear in solution-aged alloys.The primary precipitated phases areη’（Mg Zn₂）when Li content is less than 1.0 wt.%.Nevertheless,the main precipitated phases of the 7075-2Li alloys areδ’（Al₃Li）andη’（Mg Zn₂）phases disappear.As the Li content increases,the hardness,tensile strength,and wear resistance of the alloys first increase and then decrease,but the elongation of the alloys decreases gradually,and the alloys exhibit brittle fracture.7075-1Li alloys have the best mechanical properties and wear resistance,with a hardness of 134.44 HV,a tensile strength of434 MPa,and a wear rate of 2.09×10^-3 mm³·N^-1·m^-1.The alloys all experience oxidative wear and abrasive wear,and gradually change from slight adhesive wear（7075-0.25Li）to non-adhesive wear（7075-1Li）and then gradually to severe adhesive wear（7075-2Li）.