| Spray forming process is an innovative technique to manufacture high strengthaluminum alloys. Porosity is always present in the spray formed materials. So thethermomechanical densification process is applied to meet the requirements for structurematerials. Hot rolling process is a significant densification technique for aluminum alloys,which can eliminate porosity in spray formed materials and manufacture plates and stripswithin one step. It has advantages of energy saving and short production run. In this study, themicrostructures of as-deposited, as-rolled and heat treated spray formed2124aluminumalloys were analyzed by using optical microscopy (OM), scanning electron microscopy(SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and energydispersive spectroscopy (EDS). And their mechanical properties were measured by density,hardness and tensile tests. Densification and plastic deformation behaviors of spray formed2124aluminum alloy during hot rolling were investigated. The evolution of2124aluminumalloy’s microstructures and mechanical properties in the whole process from spray forming tohot rolling and heat treatment were summarized, and the optimum hot rolling processparameters and heat treatment parameters were obtained. The main results are summarized asfollows:(1)2124aluminum alloy billets were prepared by spray forming process. Themicrostructures of as-deposited billet are composed of equiaxed grains (the sizes of grains arebetween20μm to30μm) and lots of second-phases are dispersed in the matrix. The billetshave no macro-segregation near the grain boundary. The main precipitate phases were CuAl2with a small amount of Al2CuMg. However, the relative density of as-deposited billet is only90.6%. So there are some pores in the billet.(2) The optimum rolling temperature for spray formed2124aluminum alloy is450℃.Tensile strength, yeild strength and elongation of the alloy increase with increasing rollingdeformation degree. When the rolling deformation extent reaches80%, a fully dense alloyplate can be fabricated. Lots of Al2CuMg precipitate, which is the main strengthening phaseof the alloy. After hot rolling, tensile strength, yield strength and elongation of the alloy are389MPa,305MPa and14.1%, respectively. If the samples were taken along the radialdirection of a deposit before rolling, their strength and ductility after rolling are higher thanthose taken along the height direction of the deposit.(3) The hot rolling of spray formed porous materials can be divided into two stages:densification stage and plastic deformation stage. At the first stage, densification is predominant. The densification rate is higher as the large pores are closed when the totaldeformation extent is less than50%. However when the total deformation extent is up to50%,pores in the strips can be eliminated almost completely. At the second stage, plasticdeformation is predominant. When the rolling deformation extent is more than50%, theplastic deformation extent of alloy increases with increasing rolling deformation extent.(4) After the as-deposited billets are extruded at450℃with the extrusion ratio17, poresin alloy are almost eliminated. And then in the hot rolling process, the extruded samplesexhibit excellent formability. It can be hot rolled with nearly20%reduction for one pass. Thetotal deformation extent can reach75%and the prepared strips have excellent surface qualitywith no cracks.(5) The optimum heat treatment processing parameters for spray formed and rolled2124aluminum alloy is solution at495℃for45min and aging at190℃for9h. After heattreatment, tensile strength, yield strength and elongation of the alloy are504MPa,448MPaand11.3%, respectively. After the same treatment of hot rolling and heat treatment, tensilestrength and yield strength of cast2124aluminum alloy are18.6%and15.2%lower thanthose of spray formed alloy, and both ductility is good. Their fracture mechanisms are ductilefracture with micro-pore accumulation. |
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