Mechanical Properties And Corrosion Resistance Of 7085al Matrix Composites Strengthened By In-situ ZrB₂ Nanoparticles And Rare Earth

7085Al(Al-Zn-Mg-Cu series)alloy is a new generation of ultra-high-strength aluminum alloys for aviation and aerospace.It has high strength,fatigue resistance,high damage tolerance,and good formability.It is mainly used in large aircraft bearings.Force structures,such as key components such as spars and ribs on the Airbus A380 and Boeing 787.However,with the rapid development of a new generation of manned spaceflight,large aircraft,and carrier-based aircraft in my country,higher and higher requirements have been placed on the aluminization rate of "replacing steel with aluminum" and the performance of aluminum alloys.Alloys can no longer meet the higher performance requirements of these fields.At the same time,with the rapid development of lightweight and high-strength aluminum alloys for marine engineering and ships,it is equally important to improve the corrosion resistance of aluminum alloys.In recent years,domestic and foreign scholars have used rare earths to improve the strength,toughness and corrosion resistance of aluminum alloys,but the performance of single rare earth microalloying is limited.In this paper,the synergistic strengthening method of in-situ nano-ceramic particle composite and rare earth microalloying is used to prepare in-situ ZrB2 nano-particles and Sc,Zr synergistically strengthened 7085 Al composites,and the relationship between its microstructure,mechanical properties and corrosion resistance is studied.law,and discuss its toughening and corrosion resistance mechanism.The main findings are as follows:Microstructure of composites studies show that the in situ synthesized ZrB2 nano particles are mainly distributed on the grain boundaries,and some are distributed inside the grains.The interface relationship between matrix alloy and in-situ ZrB2 nanoparticles is a semi-coherent.At the same time,with the increase of ZrB2 content,the agglomeration phenomenon intensified.When the content was 3 wt.%,distribution of in-situ ZrB2 nanoparticles was relatively uniform,and matrix grains were the smallest with an average grain size of 50.4 μm.The compound addition of rare earth element Sc and element Zr can precipitate two rare earth nanophases,Al3 Sc and Al3(Sc,Zr)in the matrix,and produce a significant grain refinement effect,and at the same time,it also effectively refines the Mg Zn2 precipitation phase.Under the synergistic strengthening of in-situ nanoparticles and rare earths,the average grain size of the composites is refined to 20.2 μm,which is 81.2% lower than that of 7085 Al alloy.At the same time,the addition of rare earth Sc element reduces the clustering tendency of the in situ ZrB2 nanoparticles,the shape is round and the size is reduced.The mechanical properties of the composites showed that: under the synergistic strengthening of in-situ nanoparticles and rare earth,the mechanical properties of7085 Al composites reinforced by 3 wt.% ZrB2 nanoparticles and 0.5 wt.% Sc+0.3 wt.%Zr reached the best,its yield strength,tensile strength and elongation reached 643.5MPa,687.3 MPa and 11.2%,respectively,which were 27.7%,25.3% and 83.6% higher than those of 7085 Al alloy.The strengthening effect of synergistic strengthening is higher than that of single particle or rare earth strengthening phase.The analysis of the strengthening and toughening mechanism shows that the strengthening of the composites is mainly due to the refinement of the matrix grains,the Orowan strengthening,CTE strengthening and load transfer strengthening of the in-situ nanoparticles and rare earth nano-precipitates.Under the synergistic effect of the composite material,the reinforcement of the composite material is more uniformly dispersed,and the matrix grain is significantly refined,which greatly improves the toughness of the composite material.The research on the corrosion resistance of composite materials shows that the introduction of in-situ ZrB2 nanometer and rare earth Sc into 7085 Al alloy can significantly improve its corrosion resistance,the corrosion potential increases,the corrosion current density decreases,and the capacitive arc radius increases,the maximum intergranular corrosion depth is reduced.The maximum intergranular corrosion depth of the matrix 7085 Al alloy is 260.5 μm.On this basis,3 wt.% in-situ ZrB2 nanoparticles and 0.5 wt.% Sc+0.3 wt.% Zr synergistically strengthens the7085 Al composite,the maximum intergranular corrosion depth is reduced to 25.6 μm,and the maximum intergranular corrosion depth is reduced by 89.9%.The corrosion resistance after synergistic strengthening is higher than that of single strengthening phase.The analysis of the corrosion resistance mechanism shows that the in-situ ZrB2 nanoparticles are ceramics with high corrosion resistance.Under the synergistic effect of the in-situ ZrB2 nanoparticles and rare earth Sc and Zr,the grain size of the matrix is refined and the uniformity of the in-situ ZrB2 nanoparticles is promoted.Dispersing,making the precipitation phase along the grain boundary intermittently distributed,refining the η precipitation phase,and narrowing the precipitation-free zone at the grain boundary,so the corrosion resistance of the composite material has been greatly improved.