Study On Effect Of Quenching Process On Machinability Of 7A09 Aluminum Alloy

7A09 aluminium alloy belongs to the category of 7 series aviation aluminum alloy.Compared with other aluminum alloys,this series of aluminum alloy has a series of advantages,such as better thermal deformation performance,wider quenching domain,higher strength,and excellent corrosion resistance.It is often used to manufacture wing skin,girders and so on.Therefore,the alloy has great potential in aviation manufacturing.At present,the research on the alloy is still mainly focused on heat treatment and material properties,and there are few research on its machinability and surface quality.In view of this,this paper explores the corresponding machinability and surface quality by changing the alloy quenching process.Firstly,the 7A09 aluminum alloy was treated by oil quenching,water quenching and double liquid quenching respectively.The second phase characteristics of the alloy were observed by scanning electron microscopy.It was found that the compounds were arranged along the rolling direction after crushing.The dispersion of the second phase in the double liquid quenching state was the largest and uniform,followed by the water quenching state,and the second phase of oil quenching state was obviously less and unevenly distributed.With the help of micro vickers hardness tester,the hardness values of the three quenched 7A09 aluminum alloys were tested,and the conclusions were consistent with the conclusions of the microstructure,that is,the hardness values were as follows: double liquid quenching state?water quenching state?oil quenching state.Secondly,the dynamic mechanical behavior of 7A09 aluminum alloy could be obtained by quasi-static compression and dynamic impact tests.That is to say,7A09 aluminum alloy had not yet shown yield phenomenon under the quasi-static compression test,but work hardening had already appeared.The reason was that when the material underwent plastic deformation,its internal lattice had serious distortion,which also had a certain hindering effect on the internal slip of the material.At the same time,the flow stress of the alloy increased with the increase of strain rate,which led to strain rate strengthening effect.When the impact temperature was higher,the material would show a significant thermal softening effect.The corresponding Johnson cook constitutive parameters of the three quenched workpieces could be obtained by the variable separation method and the nonlinear fitting method.Then,the Johnson-Cook constitutive parameters were imported into Deform-3D finite element software,and the cutting simulation is carried out.The corresponding stress field and temperature field distribution could be obtained,and the corresponding change rules of cutting force and cutting temperature were known when the cutting parameters were changed.During cutting,the stress distribution could be obtained as follows: The stress distribution in the second deformation zone was relatively uniform.The stress distribution in the first deformation zone was very uneven and its change gradient was relatively large.At the same time,the maximum stress was also distributed in this zone.The temperature of the workpiece during cutting was basically slightly higher than the normal temperature,while the temperature of the chips was relatively higher,and the temperature of the tool tip was the highest of the three places.The double liquid quenched workpiece had the highest hardness,which caused its cutting force and cutting temperature to be higher than the other two quenched workpieces.Finally,the simulation results were verified by experiments,and the processed surface quality of the workpiece was observed and analyzed.It could be seen that although the cutting force and cutting temperature obtained by simulation were different from the experimental values,they were all within the allowable range.At the same time,increasing the cutting speed and decreasing the feed could improve the machined surface quality,but the cutting depth had little effect on it.Because the oil quenched workpiece had the lowest hardness and the highest plasticity,the plastic deformation during cutting was also the most serious.Therefore,the oil quenched workpiece had worse surface quality than the other two quenched workpieces.