Thick Aluminum Alloy Plate Quenching Process And The Pre-stretch Hot - The Power Of Simulation And Experimental Study

Aluminum alloy 7075 thick plate stretched with high strength and toughness and low residual stress is the necessarily key material for modern aerospace and weapon industry. The strength of this alloy is greatly improved after the solution of heat treatment, quenching and age-harding. Whilst the rapid cooling ensures good mechanical properties, the thermal gradient can be large enough to produce high levels of residual stress. Reducing the cooling rates during the quenching can cut down the magnitude of residual stress, however it can also be detrimental to mechanical properties.In order to obtain thick plate which is not only the mechanical properties can be ensured, but also the residual stress can be sharply reduced, is becoming an urgent problem to be solved.The proposed method of pre-stretching is one of the most typically effective technologies to eliminate residual stress. Pre-stretching means that total-strain from 1.0% to 3.0% should be applied to quenched plates before ageing process.The main contents of the degree thesis are as follows:First, according to the basic heat transfer differential equations, the mathematic model of one-dimentional is founded. Wth the software of MATLAB, we've got the heat transfer coefficient and it is used as boundary condition for finite element model of heat fields.Second, the computational models of heat fields, stress fields and pre-stretching fields for aluminium alloy 7075 thick-plates are established by the Finite Element Analysis Software MSC. Marc. The effects of material characteristics which are along with the temperature are considered.Third, with the metod of finite element, the principles which are affecting on residual stress in aluminium alloy 7075 thick-plates have been studied and concluded under different pre-stretching techniques, the rate of abatement has been calculated too. Pre-stretching can not only eliminate the rolling direction of residual stress, but also enable the horizontal direction of the residual stress significantly lower than that.Fourth, the results of equivalent strain contours of aluminum alloy are obtained, it is clear that plastic strain far from clamped zone is uniform (almost equal to the amount of each pre-strain), whereas plastic strain close to clamped zone is uneven and dramatic changes. In addition, it's easy to identify unqualified area where plastic strain is more than 3.0% which is as a guideline for the cutting law. And the rates of cutting region are calculated when some of the clamps are failture during the aluminum alloy ultra-thickness plates are stretching.Fifth, In order to verify the simulation results, the quenching and the pre-stretching test platform of aluminium alloy 7075 are set up. With the method of crack compliance method, the residual stress which is before pre-stretching and after pre-stretching can be measured. Comparison with the experimental results and the simulation results, they are very near to each other.All above mentioned research contexts, methods and coclusions are helpful to the research on perfecting and controlling the arts and crafts of aluminum alloy 7075 thick plate stretched.