| Nowadays,cold-rolled 2024 aluminum alloy sheets are widely used in the aerospace field.As one of the typical high strength deformed aluminum alloy,aluminum alloy 2024 has the advantages of high strength,low density,excellent heat resistance and forming performance.The main production process of cold-rolled 2024 aluminum alloy sheets is:smelting and casting? homogenizing annealng?hot rolling?cold rolling?solution treatment?aging.Alloy 2024 is one kind of the aluminum alloys strengthened through heat treatment,and solution and aging are the main heat treatment strengthening processes.The good performance can be obtained via heat treatment with reasonable parameters.The alloy contains much chemical elements,and many second phase particles are therefore formed and existed in the alloy,which will affect the properties significantly.The cold-rolled sheets of the alloy usually exhibit poor properties,which can be controlled via heat treatment such as solution and aging processes.Therefore,it is of great significance to study the influence of heat treatment parameters on the properties and the microstructure of the alloy.In this study,the effects of heat treatment parameters on microstructure of the alloy including grain structure,second phase particles and texture were characterized and analyzed in detail.In addition,the mechanical properties were tested and the fracture morphology was observed.Tne heat treatment process parameters were optimized according to the results for good comprehensive properties.This study provides theoretical guidance for the heat treatment process of the cold-rolled 2024 aluminum alloy sheets.The main works of this study are as follows:(1)The orthogonal test of four factors and five levels was designed for the solution and aging process of cold-rolled 2024 aluminum alloy sheets.The range,analysis for the orthogonal test results was carried out.Consequently,the optimum parameters and the magnitude of their influence on the properties were obtained.The effect curve of the properties vs.heat treatment parameters was plotted,based on which the significance of different parameters effect on the properties was studied.The optimal heat treatment parameters were obtained with a comprehensive balance method.(2)The effects of solution and aging parameters on the properties were investigated by means of a control variable method.The relationship table between the heat treatment parameters and the properties was established.It is found that the shorter aging time is needed to reach the peak strength at the higher aging temperature.And at the high aging temperature the properties change more obviously with the aging time.(3)The effects of solution and aging parameters on the grain structure,second phase particles,texture and fracture morphology of the alloy 2024 sheets were studied by means of the control variable method.The microstructure exhibits the larger average grain size when the alloy was soluted at higher temperature for longer time.And the particles including S and ? phases can be dissolved more fully at the high solution temperature for long time.The main texture types in the alloy after solution treatment are R,S and Cube textures.At the beginning of the artificial aging,the number of GPB zones and S phase increase with the aging time.The number of GPB zones still decrease after reaching peak aging,while the number of S phase increases and the its size increases simultaneously.The precipitate free zone(PFZ)on the grain boundary appears,and the width increases gradually with the aging time.For the aged alloys,the fracture surface exhibits dimples and tearing edges,which suggests the ductile fracture occurs.There are fewer and shallower dimples on the fracture surface at longer aging time. |
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