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晶粒尺寸及Taylor因子對(duì)過時(shí)效態(tài)7050鋁擠壓型材橫向力學(xué)性能的影響
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更新時(shí)間：2015-11-19
采用常溫沖擊實(shí)驗(yàn)和拉伸實(shí)驗(yàn)研究了大斷面7050 鋁合金型材橫向3 個(gè)典型位置的力學(xué)性能的差異，并通過OM、EBSD 和TEM分析了其顯微組織。
晶粒尺寸及Taylor因子對(duì)過時(shí)效態(tài)7050鋁擠壓型材橫向力學(xué)性能的影響EFFECT OF GRAIN SIZE AND TAYLOR FACTOR ON THE TRANSVERSE?MECHANICAL PROPERTIES OF 7050 ALUMINIUM ALLOY EXTRUSION?PROFILE AFTER OVER-AGING
采用常溫沖擊實(shí)驗(yàn)和拉伸實(shí)驗(yàn)研究了大斷面7050 鋁合金型材橫向3 個(gè)典型位置的力學(xué)性能的差異，并通過OM、EBSD 和TEM分析了其顯微組織。結(jié)果表明：晶粒尺寸約 12μm的型材芯部比晶粒尺寸約 6μm的邊部的屈服強(qiáng)度高，其原因是芯部較硬 copper 取向的形變織構(gòu)組分更強(qiáng)。根據(jù)固溶合金元素含量所得的固溶強(qiáng)化項(xiàng)、亞晶粒尺寸所得的晶界強(qiáng)化項(xiàng)和合金的屈服強(qiáng)度可計(jì)算 Taylor 因子，芯部為3.925，邊部為2.257。晶界強(qiáng)化模型中Hall-Petch 模型比 Nes模型更適用于計(jì)算固溶后的晶界強(qiáng)化對(duì)合金屈服強(qiáng)度的貢獻(xiàn)。此外，還建立了3 種試樣過時(shí)效態(tài)沖擊功與亞晶粒尺寸之間的線性關(guān)系。
Generally, it is believed that inside the material the smaller grain size is, the higher yield strength is.?In addition to this effect, grain refinement method also ensures that the toughness of the material is not reduced.?However, it is found that the relationship between the grain size distribution and mechanical properties is?contradiction with this law after the properties have been studied in the transverse direction of a large?cross-section 7050 aluminum alloy profile. That is the impact energy and yield strength in the center with a large?grain size is higher than those at the edge with the smaller grain size in the thickest section of the profile. Besides?that, during the establishment of the yield strength model in over-aging 7050 aluminum alloy, there are two?models for the grain boundary strengthening which are Nes model and Hall-Petch model, so the choice from these?model is bound to affect the final results of the yield strength model. In order to study and understand the reasons?for this phenomenon, the difference of mechanic properties distribution in the cross-section of 7050 aluminum?extrusion profile has been investigated by impact test and tensile test at normal temperature, meanwhile, the?microstructures have been analyzed by optical microscopy, electron back-scatter diffraction and transmission?electron microscope. The results show that lots of the harder deformation texture i.e. Copper texture in the core of?the profile leads to higher yield strength in the core with grain size of 12 μm than that in the edge with grain size?of 6 μm. And the Taylor factor could be calculated after the solution strengthening by alloying elements, grain?boundary strengthening by the sub-grain and the yield stress of the alloy. At last, it reaches to 3.925 in the core,?while that is just 2.257 in the edge. Compared with Nes model, the Hall-Petch model is much preferable to the?calculation of grain boundary strengthening in yield stress of 7050 aluminum alloys after solid solution treatment.?It is established that there is a linear relationship between impact toughness and grain size of three over-aging?specimens.?
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