Cd对铸造Al-Si-Cu-Mg合金时效过程的影响

合金元素Cd的添加促进了铸造Al-Si-Cu-Mg合金的时效过程，提高了合金的峰时效硬度，加快了合金的硬化速度．当加入0．27％Cd时，合金的强度提高了20％；但加入量继续增大，强度反而降低．SEM，DSC和TEM分析显示，Cd加快了亚稳相的析出，较早地形成了细小而密集的亚稳相；同时，较大的富Cd相、少量稳定相和过剩硅相质点的均匀析出，对合金起到了第二相强化的作用．在这两类析出相的共同作用下，合金获得了高的峰时效强度．但当合金中Cd的含量超过0．27％时，会形成一些富Cd的多元相和纯Cd质点，这些相的出现导致了合金机械性能的下降．     

Zr对铸造Al-Si-Cu-Mg合金时效硬化行为的影响

利用硬度测试、拉伸测试、DSC、TEM等手段研究了不同Zr含量对铸造Al-Si-Cu-Mg合金的强化相时效析出的影响。结果表明：Zr在不同时效期间的作用不同,前期推迟GP1区的形成,峰值时效期间促进富Cu相的析出,时效后期抑制富Cu相向平衡相转变;Zr的加入提高了合金的力学性能。     

稀土对Al-Si-Cu-Mg合金组织和性能的影响

微量稀土对Al-Si-Cu-Mg铸造合金的影响是多方面的,除具有细化初生α-Al相颗粒外,还能对共晶硅相起变质作用,显著提高合金的力学性能.随着合金中稀土含量的增加,稀土元素在合金中的存在形式发生变化.稀土元素能够与合金中的多种元素形成化合物,当含量过量时会有一些富稀土元素的粗大块状多元相和纯稀土质点出现.微量稀土能够影响合金的时效过程,稀土的加入能提高合金峰时效硬度,减小Al-Si-Cu-Mg合金的时效速度,推迟合金时效硬化峰的到来,延缓合金的过时效软化.     

含Er和Zr元素的Al-Mg-Si合金板材时效析出与强化行为

通过研究热处理工艺对Al-Mg-Si-Zr-Er合金组织与性能的影响,确定了合金板材的峰时效热处理工艺,探讨了合金的析出与强化行为。研究结果表明:540℃固溶1 h后,合金板材的析出相得到充分溶解,再结晶组织也未发生明显粗化;时效时,合金的析出相主要为Mg2Si、Al Cu Mg Si(Q相)和Cu Al2等;Er和Zr元素的加入促进了β″相析出,并使β″相变得更为细小弥散,从而缩短了时效时间,提高时效强化效果;合金的峰时效工艺为540℃固溶1 h,180℃时效5 h;合金的时效强化是位错切过机制和绕过机制的综合作用;合金的较高强度源于合金凝固组织细化、Al3(Er,Zr)粒子的弥散强化以及Er和Zr元素的加入促进β″相析出细化等共同作用的结果。     

预拉伸处理对2024铝合金组织和性能影响

采用硬度测试、室温力学性能测试、组织观测,研究了自然时效前的预拉伸(预拉伸率1%、1.5%,2%、2.5%、3%)对2024铝合金时效过程和拉伸性能影响。结果表明,预拉伸处理延缓了合金的自然时效过程,但提高了合金的硬度和强度。当预拉伸率为2%时,合金的最高强度和伸长率分别为456 N/mm2,20.6%,这是由于冷变形量不同、回复所引起的软化、GPB区和S″相强化综合作用所导致的。自然时效时,析出物为GPB区、T相(Al20Cu2Mn3)及S″相(Al2CuMg),其中GPB区、S″(Al2CuMg)相为主要强化相,T相(Al20Cu2Mn3)有细化晶粒的作用,比未预拉伸处理合金的析出相数量多,且析出相分布更均匀,使合金厚板的强度提高。     

高温合金的强化

正通常采用复杂的合金化,通过固溶强化、第二相强化(时效沉淀强化)和晶界强化的原理达到强化。(1)固溶强化:合金元素(W、Mo、Cr等)加入到镍铁钴高温合金中形成单相奥氏体而强化,其使晶格畸变及降低固溶体中元素的扩散系数来阻止滑移,提高热强性,多元素的作用更显著。(2)第二相强化(时效沉淀析出强化):是高温合金的重要强化方式,通过第二相强化或析出弥散质点     

微合金化元素Sn对Al-Mg-Si合金高温时效强化相析出路径的改变

研究了Sn(0.2%,质量分数)的添加对一种富Mg的Al-Mg-Si合金经历不同时间的自然时效后在250℃下人工时效过程中的时效硬化行为的影响,并利用TEM观察揭示了其微观机理。结果表明,在Al-Mg-Si合金中添加微量Sn(0.2%)可以改变合金250℃人工时效的强化相析出路径:当直接进行人工时效时,析出相主要为b"相;当进行自然时效+人工时效处理时,随着自然时效时间的延长,b"相的比例不增反降,而b'相的比例不降反增,但最终b"相的比例仍高于b'相的比例。Sn对强化相析出路径的改变,可以明显提高合金高温人工时效的硬化能力。Sn的添加提高了基体中有效的Si浓度,从而改变了不含Sn合金的强化相析出路径。     

2A70铝合金环件胀形强化微观机制的试验研究

结合2A70铝合金环件胀形工艺研究的需要,采用拉伸试验、扫描电镜、透射电镜研究胀形强化的微观机制。结果表明:经过胀形工艺的铝合金环件拉伸强度明显提高,但伸长率略有下降;胀形工艺为合金引入大量位错,有利于基体中空位和溶质的扩散,促进合金强化相—S相的均匀析出,并使无沉淀析出带变窄;大量弥散分布的S相缩小第二相质点间距,位错绕过质点应力增大,有利于提高合金的强度;较窄的无沉淀析出带会导致塑性下降。     

Fe-1.18Cu合金的时效强化

含铜高纯低碳钢具有高强度、高韧性等多种优良的性能，研究铜在钢中的沉淀规律具有重要意义。本文借助JEM-2010高分辨透射电镜研究了Fe-1．18Cu合金的时效组织，初步探讨了其时效强化机制。结果发现，在时效峰处，在铁素体基体上析出亚稳富铜颗粒。这种富铜过渡相形成的GP区对合金起强化作用。在时效过程中，析出颗粒周围存在着高密度的位错和层错。析出颗粒阻碍位错运动，提高合金的强度。     

异相强化对Al-Cu-Mg系合金高温性能的影响

Al-Cu-Mg系合金是靠时效强化提高耐热性,但这种强化作用在200℃以下较为适宜,如果,使用温度提高,耐热性明显下降.在250℃下进行持久试验发现:α(Al)过饱和固溶体已经分解,S(CuMgAl_2)相质点沿晶界析出;在300℃下,进行持久试验发现:S(CuMgAl_2)相大量析出,并聚集长大.这说明当温度达到250℃以上时,由于S(CuMgAl_2)相大量析出并聚集,合金的耐热性降低.而在Al-Cu-Mg系合金中,等量地加入Fe和Ni(0.8～1.2%),在基体内形成FeNiAl_9相,就能提高合金的耐热性.在250℃下,进行持久试验发现:FeNiAl_9相的形态无变化;在300℃下,进行持久试验发现:FeNiAl_9相的形态仍无变化.随着温度的升高,FeNiAl_9相的形态不发生变化,因而,对合金的耐热性有良好的作用.FeNiAl_9相就是起异相强化作用,试验表明:在Al-Cu-Mg系合金中,等量加入Fe和Ni,能使合金的高温性能提高2～4千克/毫米~2.     

Effect of Cd and Sn Addition on the Microstructure and Mechanical Properties of AI-Si-Cu-Mg Cast Alloy

AMONG the commercial aluminum cast alloys,Al-Si-Cu-Mg alloy is extensively used mainly becauseof its good castability and excellent mechanicalproperties in the heat treated condition[1,2].It isaccepted that two precipitation sequences are mainlyresponsible for the precipitation hardening ofAl-Si-Cu-Mg alloy[2-4],namely:—GP zonesphase and-*GP zonesphase.Where GPs are the Cu/MgGuinier-Preston zones,P"/9"and/9'are themetastable p h a s e s,a r e equilibrium phaserespectively.It is well …     

Effect of Cd and Sn Addition on the Microstructure and Mechanical Properties of Al-Si-Cu-Mg Cast Alloy

The present work has investigated the effect of trace elements Cd and Sn on the microstructure and mechanical properties of Al-Si-Cu-Mg cast alloy. With the increase of Cd addition the strength of alloy rises at first and then drops. The optimal amount of Cd and Sn addition for AI-Si-Cu-Mg alloy is about 0.27% and 0.1% respectively. Due to the formation of some coarse Cd-rich phases and pure Cd particles the mechanical properties of alloy decrease when Cd amount exceeds 0.27%. When more than 0.1% Sn added, some Sn atoms form low-melting eutectic compound at grain boundary, and then cause over-burning in alloy when solution treated, which may deteriorate properties of alloy, especially ductility of alloy.On the other hand, the addition of Cd and Sn remarkably increases the peak hardness and reduces the time to reach aging peak in Al-Si-Cu-Mg alloy. The action of Cd/Sn in quaternary Al-Si-Cu-Mg alloy is effectively the same as that occur in binary Al-Cu alloy that the enhanced hardening associated with Cd/Sn addition is due to the promotion of the θ‘phase.     

Effects of Y content on microstructures and mechanical properties of as-cast Mg-Zn-Nd alloys

The effects of Y addition amount on the microstructures and mechanical properties of as-cast MgZn-Nd alloy have been investigated by using an optical microscope, a scanning electron microscope, backscattered electronic imaging technique, an X-ray diffractometer, a differential thermal analyzer and a universal testing machine. There are three kinds of ternary phases in the Mg-Zn-Y system alloys, such as I phase(Mg3Zn6Y), W phase(Mg3Zn3Y2) and Z or X phase(Mg12Zn Y). The experimental results in the present study indicate that the Mg-Zn-RE(RE includes Y and Nd) ternary phases change from the I + W phases in turn to unique W, W + Z and unique Z as the Y content increases from 0% to 3%. Simultaneously, their distribution gradually changes from small particle-like form to continuous network form. The grain size first decreases as the Y content increases from 0% to 1% Y, then increases when the Y content exceeds 1% and finally decreases again when the content exceeds 3% due to the variation of growth restriction factor caused by the increased Y element and the change of the ternary phases. The hardness continuously increases because of the increased ternary phase amount. The ultimate tensile strength and elongation first increase within the range of 0-1% Y, also due to the increased ternary phase amount and grain refinement, and then decreases because of the grain coarsening, porosity formation and continuous network distribution of the ternary phases. The grain bonding strength of the W phase-containing alloys is quite strong and the W phase is an ideal strengthening phase if a given amount of it distributes in discontinuous and small-sized form. The alloy with 1% Y only has one ternary phase of W, but has the best combination of mechanical properties. The fracture regimes of these alloys always present a transgranular mode.     

Neodymium-rich precipitate phases in a high-chromium ferritic/martensitic steel

Neodymium being considered as nitride forming element has been used in a design of advanced ferritic/martensitic (FM) steels for fossil fired power plants at service temperatures of 630 °C to 650 °C to effectively improve the creep strength of the steels. To fully understand the characteristics of neodymium precipitates in high-Cr FM steels, precipitate phases in an 11Cr FM steel with 0.03 wt% addition of Nd have been investigated by transmission electron microscopy. Three neodymium phases with a face-centered cubic crystal structure and different composition were observed in the steel. They consisted of neodymium carbonitride with an average lattice parameter of 1.0836 nm, Nd-rich carbonitride mainly containing Mn, and Nd-rich MN nitride mainly containing Mn and Co. Other three Nd-rich and Nd-containing phases, which appear to be Nd-Co-Cr/Nd-rich intermetallic compounds and Cr-Fe-rich nitride containing Nd, were also detected in the steel. Nd-relevant precipitates were found to be minor phases compared with M₂₃C₆ and Nb/V/Ta-rich MX phases in the steel. The content of Nd in other precipitate phases was very low. Most of added Nd is considered to be present as solid solution in the matrix of the steel.     

烧结NdFeB磁体热压变形后富Nd相的显微组织

采用热压变形法对NdFeB磁体晶间富Nd相的显微组织进行了研究,实验结果表明,NdFeB磁体经真空热压变形后,富Nd相不再平均地分布在磁体晶间,而是聚集成团块状或从磁体边缘渗出,显微组织分析表明,富Nd相主要是由α-Dd和Nd2Fe17两相组成,与Nd-Fe合金的共晶组织成分接近,对于晶间添加Al元素的磁体,Al溶入晶间形成Nd2Fe15Al2相弥散地分布在晶界上,这有益于磁体矫顽力的提高;对于晶间添加Cu元素的磁体,晶间没有发现有新相产生。     

不同热成形工艺下TA32钛合金的流变性能及组织演变

用OM,SEM和XRD等方法研究了挤压态Mg-Al-Ca-x Nd(x=0~1.76,质量分数,%)合金的显微组织和析出相以及该合金在室温和高温下的力学性能。结果表明,Nd的添加会使基体中形成Al2Nd和Al11Nd3相,并且细化Mg-Al-Ca合金的晶粒。随着Nd添加量的增加,Al2Nd和Al11Nd3相的数量也随之增加。当添加1.76%Nd时,合金的平均晶粒尺寸从不含Nd的4.80μm变为2.39μm。由于第二相的析出和晶粒细化,室温下的力学性能也得到改善。随着Nd元素含量的增加,合金的室温抗拉伸强度由267MPa提高到304 MPa,屈服强度从144 MPa提高到203 MPa,延伸率从20.0%下降到16.9%。在150℃时,随着Nd含量的增加,拉伸强度从192 MPa增加到229 MPa,屈服强度从140 MPa增加到159 MPa,伸长率从48.6%下降到29.3%。     

Nd_(90)Al_(10)晶界调控对晶界扩散磁体磁性能和微观结构的影响EI北大核心CSCD

采用添加Nd_(90)Al_(10)低熔点合金调控制备了扩散用烧结Nd_2Fe_(14)B磁体,并采用Tb晶界扩散制备了相应的扩散磁体,分析了扩散磁体的晶界结构和成分对磁体矫顽力的影响。结果表明,添加质量分数为0.5%的Nd_(90)Al_(10)合金调控后,晶界扩散(GBD)后磁体的矫顽力提高到1439 kA/m,相对于未晶界调控的扩散磁体增加了530 kA/m。添加Nd_(90)Al_(10)低熔点合金不会影响GBD前磁体的Curie温度,但降低了磁体的低温相变温度。GBD后磁体Tb取代晶格中的Nd引起Nd_2Fe_(14)B相的晶格常数减小,从而使XRD谱中衍射峰位右移。经Nd_(90)Al_(10)调控后的扩散磁体表面处的主相晶粒的富Tb壳清晰可见。从距离磁体表面20μm增加到100μm时,富Tb壳层仍清晰可见。当深度继续增加到500μm时,经Nd_(90)Al_(10)调控后的扩散磁体晶粒周围都有连续晶界相。经晶界调控的扩散磁体可见衬度明显的富Tb壳层,形成了非晶的富Nd相,增强了两两主相晶粒间的去磁耦合能力。Nd在富Nd相中心区域出现峰值,更多的富Nd相在晶界扩散过程中作为Tb向磁体内扩散的通道,Tb原子在富Nd相的浓度高达约35%,其扩散深度和使用效率明显提升。     

Microstructure and strengthening mechanisms of Mg-6Al-6Nd alloy

The microstructure and strengthening mechanisms of as-cast Mg-6Al-6Nd alloy were studied. The results show that the addition of 6 wt.% Nd into Mg-6Al alloy leads to the precipitation of Al11Nd3 and Al2Nd phases and decrease in the content of Al solid soluted in Mg-Al matrix. The volume fractions of Al11Nd3 and Al2Nd phases are 3.64% and 0.34%, respectively. Compared with Mg-6Al alloy, the ultimate strength, yielding strength, and elongation of Mg-6Al-6Nd alloy at room temperature and 175°C are enhanced in some degrees. The strengthening mechanisms of Mg-6Al-6Nd alloy are mainly composed of solid solution strengthening of Al solid soluted in Mg-Al matrix and grain refinement strengthening, dispersion strengthening, and composite strengthening brought by the precipitation of Al11Nd3 phase. The composite strengthening includes the load transfer from the matrix to Al11Nd3 phase and the enhancement of dislocation density due to the geometrical mismatch and thermal mismatch between the matrix and Al11Nd3 phase.     

不同RE含量对Al-Cu-Mn合金组织和性能的影响

通过力学性能检测和金相显微观察,研究了混合稀土含量(质量分数:0,0.4％,0.8％,1.0％)对铝铜合金组织和性能的影响.结果表明,混合稀土加入量对Al-4.5％Cu-0.7％Mn合金的组织和性能有很大的影响.随着混合稀土加入量的增加,合金的抗拉强度快速增加,在混合稀土含量0.4％时达到峰值;稀土含量进一步增加,晶粒有粗化趋向,抗拉强度随之下降.随着混合稀土加入量的增加,合金基体显微硬度快速下降.