High Strength Aluminum Alloy Thick Plate Forging New Organizational Evolution And Quenching Residual Stress Research

With the growth of the national economy and the rapid development ofscience and technology, high strength and toughness resistance to corrosionaluminum alloy thick plates and middle-thick plates have gradually become theimportant structural materials in aerospace、shipbuilding、transportation anddefense equipment and other areas. The preparation of high-performanceprocessing of the aluminum alloy thick plate relates to the melting and casting,plastic working, heat treatment and machining, etc. In order to achieve theproduction of the aluminum alloy thick plate, a systematic study is also neededon the basic theories of alloying theory, strengthening mechanisms duringplastic deformation and heat treatment processes, microstructure evolution andquenching residual stress.The paper focuses on several processing technologies in the preparation ofhigh-strength aluminum alloy thick plates, taking the alloy with as-cast,as-forged, as-aged and as-overaged four different initial structures as testingmaterials，hot compression tests with constant temperature and strain rate havebeen conducted on GLEEBLE-1500D thermo-mechanical simulator attemperatures in the range of300℃～420℃, strain rates in the range of0.01s-1～1s-1and20%～80%reductions. Flow stress behaviors were analyzed.Microstructure evolution of all four kind samples has been analyzed bymicroscopes. And the distribution of quenching residual stress in thehigh-strength aluminum alloy thick plates is analyzed by the finite elementnumerical simulation, and the cold compression method is used to eliminatequench residual stresses. The main contents and conclusions as follows:1. By the comparative analysis of flow stress behaviors of four different initialstate of the new high-strength aluminum alloy, it can be seen that the influenceof different deformation conditions on the alloy flow stress is significant. In thesame deformation conditions, flow stress behavior of as-forged samples is muchsmaller than that of as-cast samples, and similar to that of as-over-aged samples. The flow stresses of as-over-aged samples are much larger than that of theas-aged samples. The flow stress can be described by Arrhenius equationcontaining Zener-Hollomon parameter as follows:a. as-cast：（ε|·）=1.025×10²¹[sinh（0.00964σ）]^7.0097exp（269.985/RT）b. as-forged：（ε|·）=1.659×10¹⁴[sinh（0.01096σ）]^5.8111exp（188.873/RT）c. as-aged：（ε|·）=1.421×10¹⁹[sinh（0.0923σ）]^6.4525exp（247.457/RT）d. as-overaged：（ε|·）=2.463×10¹³[sinh（0.01108σ）]^5.6459exp（178.252/RT）2. By observing the hot deformation microstructures of four different highstrength aluminum alloy samples, it shows that dendritic grains disappearedand dynamic recovery occurs mainly in as-cast samples; the refining andhomogenization is low；For as-forged samples, dynamic recrystallization occursat the certain temperature and strain rate conditions, new small and uniformrecrystallized grains are generated when reduction is large enough. For as-agedsamples, the elongated microstructures transform to equiaxed shape gradually,the content of precipitated phase is less；the quantity of the precipitated phasesof as-overaged samples is more，recrystallization fraction of hot deformationmicrostructure is larger，new recrystallized grains are small and uniform.3. The recrystallization annealing processes of work hardening samples withas-forged and as-overaged starting structure deformed at lower temperatures andhigher strain rates were carried out. Static recovery and recrystallization occur.4. The temperature and stress fields of a new Al-Zn-Mg-Cu high strengthaluminum alloy thick plate were simulated by the Simufact FE-software.Because of the temperature gradient and the integrity limit of thick plates,residual stress distribution in the thick plate is characteristic by compressivestresses on the surface areas and tensile stresses in the center areas afterquenching. The value of maximum tensile stress in the center areas of the plateis about199MPa, and the value of maximum compressive stress on the platesurfaces is about-175MPa. Residual elimination of quenched plates by coldsymmetrical compression method was simulated by the FEA. Throughsimulation analysis, it shows that residual stresses can be eliminated about90% under the compression conditions of1%～3%reduction and75%feeding ofanvils.