冷却速度对Al-3Fe合金凝固特性和微观组织的影响

采用冷却曲线测定、光学显微镜(OM)和X射线衍射仪(XRD)研究了冷却速度对Al-3Fe合金凝固特性和凝固组织的影响。结果表明,在冷却速度为0.69~11.8℃/s的范围内,Al-3Fe合金的显微组织均由α-Al枝晶、初生富Fe相及枝晶间的共晶组织组成,其中富Fe相主要为Al₃Fe、Al₅Fe₂和Al₆Fe相。冷却速度对Al-3Fe合金的凝固特性和凝固组织有明显的影响。随着冷却速度的提高,合金初生相形核温度和共晶反应温度降低,合金的凝固组织明显细化。     

Ce对Al-5Cu合金组织和性能的影响

通过光学显微镜、X射线衍射仪、场发射扫描电镜、能谱仪、同步热分析等手段，研究了Ce含量对Al-5Cu合金显微组织和力学性能的影响。结果表明，加入Ce元素后，除了α-Al和Al₂Cu相外还会生成针状Al₈CuCe₄相。合金固相线温度升高，液相线温度降低，凝固温度区间缩短，α-Al得以有效细化和均匀化。随着Ce含量增加，共晶Al₈CeCu₄相逐渐增多，Al₂Cu相在Al₈CeCu₄相边缘附着生长，逐渐形成了沿晶界分布的封闭网状结构。经过T5热处理后Al₂Cu相以粒状弥散析出，基体Cu含量增大，耐热性强的Al₈CuCe₄相形态基本不变。合金的抗拉强度、屈服强度和伸长率均先增大后减小。当Ce含量为0.3%时，合金力学性能最优，抗拉强度、屈服强度和伸长率分别为320 MPa、238 MPa和13.6%,较铸态的明显提高。     

高合金化Al-9Zn-2Mg-2Cu-0.3Ce合金均匀化过程中的组织演变

采用光学显微镜(OM)、扫描电镜(SEM)、电子探针显微分析(EPMA)、X射线衍射(XRD)以及差示扫描量热仪(DSC),研究了一种高合金化Al-9Zn-2.0Mg-2Cu-0.3Ce(质量分数,%)合金的铸态微观组织,以及其均匀化过程中微观组织的演变,获得了较优的单级均匀化工艺。结果表明:铸态时,合金晶粒内部枝晶网络发达,Zn、Mg、Cu元素偏聚严重,合金中主要的非平衡凝固相为T(AlZnMgCu) 相和θ(Al₂Cu)相。经过470 ℃×48 h均匀化热处理后,合金中的枝晶网络基本消除,凝固相T逐渐回溶至基体中,主要的残留相为耐高温相Al₂CuMg、Al₈Cu₄Ce和Al₇Cu₂Fe。扩散动力学分析表明,470 ℃退火48 h的单级均匀化工艺足以使合金中的非平衡相回溶至基体中。     

固溶处理对铸态Mg-4.8Al-2.7Ca-0.4Mn合金组织及力学性能的影响

采用光学显微镜、扫描电镜、X射线能谱仪、X射线衍射仪、硬度测试及拉伸性能测试等手段分别研究了铸态Mg-4.8Al-2.7Ca-0.4Mn合金固溶处理前后的组织演变及力学性能。结果表明,铸态Mg-4.8Al-2.7Ca-0.4Mn合金的微观组织中,α-Mg相呈现典型的枝晶形态,枝晶间分布着大量在凝固过程中形成的Al₂Ca相;固溶处理对第二相的形貌有显著影响,随着固溶时间的增加,枝晶偏析减弱,Al₂Ca相从网状分布演变为多边形或细块状;经500 ℃固溶4 h,合金具有较好的综合拉伸性能,抗拉强度、屈服强度及伸长率分别达到222.0 MPa、182.5 MPa和4.5%。     

冷轧及热处理对Al0.3CoCrFeNi高熵合金组织及性能的影响

利用X射线衍射仪、扫描电镜、透射电镜和拉伸试验等手段,研究了75%压下量的冷轧及1073 K下保温1 h热处理后不同冷却方式(空冷和炉冷)对Al_0.3CoCrFeNi高熵合金微观组织和力学性能的影响。结果表明:铸态以及冷轧态Al_0.3CoCrFeNi合金均为FCC单相结构,经热处理后炉冷及空冷合金均为FCC+BCC双相结构。铸态合金经冷轧以后强度显著提升但塑性大幅度下降。因细晶强化、孪晶以及析出相强化作用,热处理后炉冷合金具有良好的综合力学性能,其抗拉强度为1289 MPa,约为铸态试样的两倍(719 MPa),最大伸长率为28.7%。因析出相增多以及孪晶尺寸增大,与空冷合金相比,炉冷合金在不损失塑性的前提下,抗拉强度增加。     

时效处理对7022铝合金组织与弯曲性能的影响

采用扫描电镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)、电子背散射衍射(EBSD)、拉伸和弯曲试验等研究了时效处理对7022铝合金组织及弯曲性能的影响。结果表明,固溶处理后7022铝合金基体中依然含有大量黑色不溶第二相,且这些相主要由α-Al、MgZn₂、Al₂CuMg和Al₇Cu₂Fe相组成。随着时效的进行,Al₂CuMg和Al₇Cu₂Fe相逐渐溶解,与MgZn₂相性质相似的Mg(Zn, Cu, Al)₂相析出,同时晶粒逐渐长大,产生明显的析出强化效应。试样的抗弯强度主要受到第二相颗粒的数目、尺寸以及晶粒尺寸的影响。110 ℃×10 h时效条件下,合金拥有弥散分布的细小第二相颗粒和合适的晶粒尺寸,具有较好的抗弯强度和抗拉强度,其数值分别为21.7 MPa、608 MPa。     

微量元素复合添加对Al-Si-Mn-Mg合金组织与强韧性的影响

为探究微量元素复合添加对Al-Si合金晶粒大小、形貌和力学性能的影响,熔炼制备了Al-8Si-0.6Mn-0.4Mg-0.15Ti-x Sc(x=0,0.2,0.4,0.5,质量分数,%,下同)合金,结合金相组织图、扫描电镜和能谱等技术手段对合金的晶粒形貌、尺寸及强韧性进行表征分析。结果表明,铸态Al-8Si-0.6Mn-0.4Mg-0.15Ti-x Sc合金的主要物相包括：α-Al基体、共晶Si相、Al₃Ti、Al₃Sc、AlMnTi、富Fe相等。Ti含量为0.15%的情况下,调整Sc含量为0.2%,可以获得最优的细化效果,合金平均晶粒尺寸为46μm,抗拉强度达到221 MPa,伸长率为5.9%。     

时效处理对深冷轧制Al-4.5Cu-1.5Mg-0.1Er合金显微组织与力学性能的影响

采用光学显微镜(OM)、X射线衍射仪(XRD)、扫描电镜(SEM)和电子万能试验机等研究了时效处理对深冷轧制Al-4.5Cu-1.5Mg-0.1Er合金板材显微组织和力学性能的影响。结果表明,经时效处理后,Al-4.5Cu-1.5Mg-0.1Er合金中析出相数量增多,分布更均匀,主要为S(Al₂CuMg)相和θ(Al₂Cu)相。随时效温度的升高及时效时间的延长,部分第二相回溶、粗化,造成合金性能下降。深冷轧制态Al-4.5Cu-1.5Mg-0.1Er合金板材经180℃×8 h时效处理后获得了最佳综合性能,抗拉强度和断后伸长率分别为541 MPa和11.33%,比深冷轧制态铝合金分别提高了58 MPa和7.11%,此时合金的断裂类型为韧性断裂。     

Al-4.5Cu-3.5Zn-0.5Mg铸造铝合金的均匀化工艺及组织演变

对Al-4.5Cu-3.5Zn-0.5Mg铸态合金进行不同双级均匀化处理,采用扫描电镜、电子探针显微分析仪、差示扫描量热仪和光学显微镜等,研究了该合金的铸态组织及其在均匀化过程中的组织演变。结果表明:铸态组织主要由α-Al、粗大Al₂Cu相以及少量AlZnMgCu、Al₇Cu₂Fe相组成,合金元素枝晶偏析严重。经470 ℃×12 h均匀化处理后,AlZnMgCu相已基本回溶至基体;第二级均匀化温度由490 ℃逐渐升高到520 ℃或者延长保温时间,Al₂Cu相逐渐回溶至基体,合金元素分布趋于均匀。合金过烧温度为520 ℃,最佳双级均匀化制度为470 ℃×12 h+510 ℃×32 h,该制度与均匀化动力学计算结果基本一致。     

Al-22Si-3Fe-1.8Mn合金中的四元富铁相研究

利用X射线衍射仪、扫描电镜(带EDS)和金相显微镜对Al-22Si-3Fe-1.8Mn合金进行研究.结果表明:在铸态试样中存在晶体结构分别与Al8Fe2Si、Al9Fe2Si2和Al3FeSi2晶体结构相同的三种四元富铁相,并确定了其中两种相的化学式分别为Al12Si2Fe2Mn、AL42.5Si11Fe4.7Mn.通过萃取态试样确定了另一种富铁相的化学式为Al15.97Sil4.8.82Fe4.24Mn,并且该相为Al-22Si-3Fe-1.8Mn合金中最先析出的高温相.     

氧化硅气凝胶对Al-4Cu-0.1Sn合金组织与性能的影响

采用铸造、冷轧和T6热处理制备了SiO₂气凝胶(SA)增强铝基复合材料。研究了SA含量对Al-4Cu-0.1Sn合金显微组织(铸态与冷轧T6态)与力学性能的影响。结果表明,SA能有效地加入到Al-4Cu-0.1Sn合金中,并以球状形式均匀的分布在晶粒内部。铸态下,随着SA含量的增加,合金的显微硬度呈上升趋势。当SA含量为0.02%时,合金平均硬度(HV)达到最高85,相对于未添加SA的合金提升了49%,但铸态下添加SA的合金拉伸性能略微下降;冷轧T6态下,当SA含量为0.02%时,合金硬度(HV)为138。随着SA增加,合金的屈服强度与抗拉强度先升高后降低,当SA含量为0.04%时,合金屈服强度达到320 MPa,抗拉强度达到401MPa,相比于未添加SA的合金提升了10.3%和10.7%。添加SA能够提高铸态Al-4Cu-0.1Sn合金硬度的机理是其细化了铸态合金的晶粒,并使晶界处第二相由粗大的骨骼状变成细小的非连续状。添加SA提高冷轧T6态强度的机理是细化了Al₂Cu相并消除了Al₇Cu₂Fe相。     

Microstructure and mechanical properties of high strength as—cast Ti—15—3 alloy

The effects of heat treatment and solidification cooling rate on the microstructure and mechanical properties of as-cast Ti-15-3 alloy prepared by induction skull melting method were investigated.Results show that the microstructure of as-cast Ti-15-3 alloy changes from the features of simplified and larger size of beta grains to finer grain size with increasing solidification cooling rate.After solution treatment and different ageing treatment,alpha phase precipitates in grains interior as well as in grain boundaries.Due to the modification of the precipitate phase,the tensile stength and elongation of the alloy are improved simultaneously.A good combination of the values of 1.406GPa of σb and 4.5% of δ was obtained,which will be satisfied the use of this kind of alloy in critical areas.     

Investigation on the microstructure and mechanical properties of a cast Mg–6Zn–5Al–4RE alloy

Mg–6Zn–5Al–4RE (RE = Mischmetal, mass%) alloy was prepared by metal mould casting method. The microstructure and mechanical properties of the as-cast and heat-treated alloys were investigated. The results show that the phase compositions of the as-cast state alloy are supersaturated solid solution -Mg, lamellar β-Al₁₂Mg₁₇, polygonal Al₃RE and cluster Al₂REZn₂ phases. The mechanical properties, especially the ultimate tensile strength and elongation of the alloy were significantly improved by the heat treatment. Fracture surface of tensile specimens was analyzed by optical microscope and scanning electron microscope.     

Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti (wt.%) alloy

The effects of different Zr additions(0.05wt.%-0.5wt.%)on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%)alloy solidified under a high cooling rate(18℃·s^-1),in as-cast and T6 heat-treated conditions were studied.The as-cast structure of the alloy consists of equiaxed grains ofα-Al with an average size of 64μm which is unaffected by the Zr additions,indicating the ineffectiveness of Zr in the grain refinement of the alloy.Scanning electron microscopy,along with X-ray diffraction analysis revealed the presence of elongatedθ-Al2Cu at the grain boundaries;in addition,coarse Al3Zr particles exist in the intergranular regions of the 0.5wt.%Zr-containing alloy.After the T6 heat treatment,the elongatedθparticles were fragmented;however,the coarse Al3Zr particles remained unchanged in the microstructure.Also,the formation of fineβ’-Al3Zr andθ’’-Al3Cu/θ’-Al2Cu phases during T6 heat treatment was revealed by transmission electron microscopy.The results of the tensile tests showed that the Zr additions increase the strength of the alloy in both as-cast and T6 heat-treated conditions,but reduce its elongation,especially with 0.5wt.%Zr addition.The 0.3wt.%Zr-added alloy in the T6 heat-treated condition has the highest quality index value(249 MPa).Fractography of the fracture surfaces of the alloys revealed ductile fracture mode including dimples and cracked intermetallic phases in both conditions.     

Effect of Partially Substituting Ca with Mischmetal on the Microstructure and Mechanical Properties of Extruded Mg-Al-Ca-Mn-Based Alloys

Mg-2Al-1.2Ca-0.2Mn(at%)-based alloys with Ce-rich mischmetal(MM) substitution of 0–0.6 at% for Ca were hot extruded at 400 °C. The effect of MM substitution on the microstructure and mechanical properties of the extruded alloys was investigated. The as-cast Mg-2Al-1.2Ca-0.2Mn alloy is mainly composed of a-Mg, Mg_2Ca and(Mg,Al)_2Ca phases and Al_8Mn_5 precipitates, whereas the substitution of MM brings about the formation of Al_(11)MM_3, Al_2MM phases and Al_(10)MM_2Mn_7 particles with the absence of (Mg,Al)_2Ca phase. The volume fraction of MM-containing phases increases with increasing MM contents. All of the extruded alloys exhibit bimodal microstructure comprising fine dynamically recrystallized grains with almost random orientation and coarse deformed grains with strong basal texture. Dense nanosized planar Al_2Ca and spherical Al–Mn phases precipitate inside the deformed grains. High tensile yield strengths of~ 350 MPa and moderate elongations to failure of 12% are obtained in all extruded alloys; the MM substitution induces negligible difference in the tensile properties at ambient temperature, while the highest MM substitution improves the strength at 180 °C due to the better thermal stability of the fragmented MM-containing phases.     

Fe含量对挤压铸造Al-3.5Mg-0.8Mn合金组织性能的影响

采用拉伸和硬度测试、扫描电镜和X射线衍射仪等手段,研究了不同Fe含量对挤压铸造Al-3.5Mg-0.8Mn合金显微组织和力学性能的影响。结果表明,Fe能改善合金的力学性能,合金中只存在Al₆(FeMn)相。合金的抗拉强度和屈服强度随着Fe含量的增加而增大,伸长率随着Fe含量的增加而降低,原因是随着Fe含量增加,硬脆的Al₆(FeMn)相增多。在挤压压力为75MPa和Fe含量为0.5%时,合金的综合力学性能最佳,其抗拉强度为252MPa,屈服强度为128MPa,伸长率为28%。     

Cu含量及T6处理对电力金具用铝合金组织性能的影响

探究了Cu含量与时效工艺对Al-Cu-Mg-Si系合金显微组织、力学性能以及耐腐蚀性能的影响。研究表明,随Cu含量的增加,铸态铝合金中Al₂Cu相数量增加、尺寸不断增大,形貌由点状转为粗网状,铸态铝合金的强度也随之提升,耐蚀性能下降。在180 ℃×(4~28) h时效区间内,整体上合金硬度先上升后下降,0.5%Cu、1.5%Cu合金在8 h时达到峰值,2.5%Cu合金在12 h时达到峰值。530 ℃固溶+180 ℃×8 h时效后,铝合金中析出Al₂Cu相,随着Cu含量的增加,Al₂Cu相的含量增加,硬度显著上升,2.5%Cu含量的合金抗拉强度达到最大值325.0 MPa,屈服强度达到258.8 MPa,伸长率为4.5%,其强度与传统的电力金具用铸铁相当。