Research On Constrained Groove Pressing Of Pure Al/Cu Sheet

Constrained groove pressing (CGP), as a kind of severe plastic deformation, can synthesize ultra-fine grained (UFG) materials, achieving higher strength and better comprehensive properties which are of great significance for transportation and aerospace industry. In this thesis, the influence laws of CGP on pure aluminum (Al)1060and pure copper (Cu) T2are mainly investigated. The changes of microstructure, mechanical properties and Vickers hardness after annealing and CGP are studied by a series of experiments. Mechanisms of these changes are analyzed. Finite element modeling (FEM) of pure Al and pure Cu subjected to CGP is done to discuss the plastic strain distribution and the influence of number of passes, groove width, groove angle and plate thickness on CGP effect, which provides scientific guidance for CGP technology and mould parameter optimization.Microstructure and grain size before and after CGP are analyzed with OM. It is showed that grain size refinement is obvious because of CGP, especially after the first pass, then it slows down during the following passes. The results of TEM showed that microstructure after CGP is the mixure of equiaxed grains and elongated grains, indicating that the microstructure is nonuniform after CGP. Mechanical segmentation plays an important role on grain refinement. Many dislocation entanglements exist in the grain or the grain boundary after CGP. The results of XRD indicate that the sheet shows anisotropy after CGP and the K-AK curve shows that after the fourth pass decrease of lattice defects and micro strain because of dynamic recovery appears to have more effect on peak width than grain refinement.Tensile test is applied on the specimens before and after CGP, showing that CGP can effectively improve the yield and tensile strength, especially after the first pass. The climbing speed of strength descends during the coming passes, even the strength goes down because of dynamic recovery or microcracks after the fourth pass. Elongation decreases comparing to annealed state, especially after the first pass. The proportion of uniform and nonuniform plastic deformation changes, indicating that CGP improves the superplasticity trend. Fracture morphology after tensile test is studied with SEM, showing that the type of fracture is ductile fracture, the size and distribution of dimples are associated with the number of passes. Vickers hardness is measured demonstrating that hardness rises after CGP, especially after the first pass, and its uniformity improves with the increase of passes.The finite element simulation of CGP on pure Al1060and pure Cu T2with software ABAQUS shows that the displacement-load curve can be divided into three stages:increase rapidly, increase slowly, and increase rapidly. The load needed of flat is bigger than that of pressing during the first two stages and it is opposite during the third stage. Equivalent plastic strain (PEEQ) in the direction of sheet thickness shows that it is more uniform in the center layer than upper and lower surfaces. In the length direction, PEEQ is unstable at two ends of the sheet and fluctuates periodically in the middle. PEEQ in the center layer is bigger than the surfaces and it distributes more uniformly in the center than the surface. Its distribution becomes more uniform as the number of passes increases. The strain accumulation effect and strain distribution uniformity on Cu are better than Al. Given the displacement-load curve, mean PEEQ and distribution uniformity, the groove width should equal to or be bigger than the sheet thickness,2mm or3mm is preference when the thickness is2mm; groove angle should be40°or45°; the sheet thickness should be close to the groove width on the premise that it is not too small,2mm or3mm is preferred when the groove width is2mm.