半固态成形Al-Fe-Cu合金组织性能及强化机理

发布时间：2018-05-12 02:09

本文选题：Al-Fe合金 + 半固态触变成形　；参考：《沈阳工业大学》2015年博士论文

【摘要】：针对常规铸造Al-Fe合金力学性能差的问题,本文开展了半固态触变成形Al-Fe基合金研究工作,研究了合金元素、半固态触变成形工艺、热处理制度等对合金组织与性能的影响,并发现了T6热处理导致半固态成形Al-Fe基合金力学性能不升反降的奇异现象,开展了合金固溶过程中的相变、时效强化相的析出特征及强化机理研究,确定了该合金反常热处理行为形成的内在机理。合金元素对Al-Fe基合金性能影响研究表明,常规铸造条件下,Cu、Zn、Mg、Mn合金元素的添加可显著提高合金的力学性能,在金属型铸造条件下,Al-5.5Fe-4Cu-2Zn-0.4Mg-0.5Mn合金的抗拉强度可达173.4MPa;T6热处理能后,合金抗拉强度明显升高,约为205.3MPa,伸长率由2.2%提高到4.0%;但T1热处理对合金力学性能的提高有限,经过160℃×6 h时效处理后,合金抗拉强度约为194.1 MPa。半固态触变成形工艺可以有效地细化Al-Fe基合金的显微组织,平均晶粒尺寸细化至7-15μm,合金力学性能得到显著提高,抗拉强度达到270.1MPa,比金属型铸造提高了约67%。对半固态触变成形Al-Fe基合金进行热处理,T6处理后工艺不但没有提高合金的强度,反而出现大幅度降低现象。在500℃×4h固溶后经165℃×6h时效处理,合金抗拉强度仅为173.8MPa,比热处理前降低了约36%;而T1处理后合金力学性能和耐磨性能均得到显著提高。对Al-Fe基合金显微组织分析表明,半固态触变成形后,合金中的富Fe相周围形成了高密度位错塞积;T6处理后,基体中Al_2Cu相发生溶解,Cu元素沿高密度位错向Al3Fe相扩散,形成一层富Cu“光圈”,Cu元素的聚集也造成了合金基体中合金元素的贫化,从而使合金失去了时效强化的作用。与此同时,固溶后合金晶粒尺寸增大,平均直径为17~20μm,这也是合金T6热处理后力学性能降低的另一个原因。XRD、DSC分析发现,半固态Al-Fe基合金在固溶过程中发生了不同于其他铝合金热处理过程的新型相变,长时间固溶热处理后,Al7Cu2Fe相在Al3Fe相周围形核长大,并形成了包裹Al3Fe相的节状相,厚度达到了500nm左右。通过第一性原理对体系总能进行了计算,由结果可知,Al7Cu2Fe相的生成热远小于Al_2Cu相,Al7Cu2Fe相的稳定性相也要大于Al_2Cu相。所以随着固溶过程Al_2Cu相逐渐溶解,Cu原子不断扩散到Al3Fe周围,形成了更为稳定的Al7Cu2Fe相,从而达到了热力学平衡状态。半固态触变成形后的Al-Fe基合金基体中,出现合金元素呈过饱和状态的现象。T1时效处理初期,在母相α-Al固溶体的{100}面上出现Cu原子聚集区,这些G.P区与母相保持共格,呈圆盘状。随时效时间的延长,Cu原子聚集区逐渐析出过渡相θ2相/θ′相,对合金基体产生有效的强化。T1处理后在晶界上析出球状和条状Al_2Cu相,对晶界起钉扎作用,阻止了合金在热处理过程中晶粒的长大;同时,基体中细小呈弥散分布的时效强化相使合金的力学性能和耐磨性得到明显提高。
[Abstract]:In view of the poor mechanical properties of conventional casting Al-Fe alloy, the research work of semi-solid thixoforming Al-Fe based alloy was carried out. The effects of alloy elements, semi-solid thixotropic forming process and heat treatment system on the microstructure and properties of the alloy were studied. The mechanical properties of the Al-Fe based alloy formed by T6 heat treatment in semi-solid forming were found to be non rise. The phase transition in the solid solution process, the precipitation characteristics of the aging hardening phase and the strengthening mechanism are carried out. The internal mechanism of the abnormal heat treatment behavior of the alloy is determined. The influence of the alloy elements on the properties of Al-Fe based alloy shows that the addition of Cu, Zn, Mg and Mn alloy elements can significantly increase the alloy element under the conventional casting conditions. The tensile strength of Al-5.5Fe-4Cu-2Zn-0.4Mg-0.5Mn alloy can reach 173.4MPa under the metal casting condition. After T6 heat treatment, the tensile strength of the alloy increases obviously, it is about 205.3MPa, the elongation of the alloy increases from 2.2% to 4%, but the improvement of the mechanical properties of the alloy by T1 heat treatment is limited. After the aging treatment of 160 C 6 h, the alloy is resistant to the alloy. The 194.1 MPa. semi-solid thixoforming process can effectively refine the microstructure of Al-Fe based alloy, refine the average grain size to 7-15 m, improve the mechanical properties of the alloy significantly and the tensile strength to 270.1MPa, and improve the heat treatment of the semi solid thixoformed Al-Fe based alloy by 67%. to the metal mold casting and T6 treatment. The post process not only does not increase the strength of the alloy, but has a large reduction in the tensile strength of the alloy. The tensile strength of the alloy is only 173.8MPa at 165 C after 4H solution at 500 degrees C, and the tensile strength of the alloy is reduced by about 36% before the heat treatment. The mechanical and wear resistance of the alloy after T1 treatment are greatly improved. The microstructure analysis of the Al-Fe based alloy shows that the microstructure of the alloy has been analyzed. After semi-solid thixotropic forming, high density dislocation plug is formed around the rich Fe phase in the alloy; after T6 treatment, the Al_2Cu phase in the matrix dissolves, and the Cu element diffuses along the high density dislocation to Al3Fe phase, forming a layer of rich Cu "ring", and the aggregation of the Cu element causes the dilution of the alloy elements in the alloy matrix, thus making the alloy lose the aging strength. At the same time, the grain size of the alloy after solid solution increases, the average diameter is 17~20 mu m, which is another reason for the decrease of mechanical properties after T6 heat treatment. DSC analysis shows that the semi solid Al-Fe based alloy has taken place in the solid solution process, which is different from other aluminum alloy heat treatment process, and long time solid solution heat treatment. After that, the Al7Cu2Fe phase grew up around the Al3Fe phase and formed a nodular phase of the Al3Fe phase, and the thickness reached about 500nm. Through the first principle, the total energy of the system was calculated. The result shows that the formation heat of the Al7Cu2Fe phase is far less than the Al_2Cu phase, and the stability phase of the Al7Cu2Fe phase is greater than that of the Al_2Cu phase. Therefore, the Al_2Cu phase is also larger than the Al_2Cu phase. So with the solid solution process Al_2Cu As phase gradually dissolves, Cu atoms continue to diffuse around Al3Fe, forming a more stable Al7Cu2Fe phase, thus reaching the state of thermodynamic equilibrium. In the Al-Fe based alloy matrix after thixotropy, the phenomenon of alloy elements appears supersaturated at the initial stage of.T1 aging treatment, and Cu atom aggregation appears on the {100} surface of the mother phase alpha -Al solid solution. In the area, these G.P regions are in common with the parent phase. With the prolongation of the aging time, the transition phase of theta 2 phase / theta phase is gradually precipitated in the Cu atom gathering area. The spheroidal and striped Al_2Cu phases are precipitated on the grain boundary after the effective intensification of.T1 treatment on the alloy matrix, and the grain boundary is pinning to prevent the grain growth from the alloy during heat treatment. At the same time, the mechanical properties and wear resistance of the alloy were obviously improved by the dispersed dispersed aging strengthening phases in the matrix.

【学位授予单位】：沈阳工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG292

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