挤压温度对Mg-Gd-Er-Zn-Mn合金力学及导热性能的影响

本文系统研究了挤压温度对Mg-8Gd-1Er-8Zn-1Mn(简称GEZM8181)合金微观组织、力学性能和导热性能的影响规律。结果表明：在325℃、350℃和375℃下挤压的GEZM8181合金分别具有双峰组织、细小完全动态再结晶组织和粗大等轴晶组织。在挤压过程中,粗大的鱼骨状W相发生破碎并沿挤压方向分布,且破碎后第二相尺寸随温度升高而逐渐增大。此外,三种合金在挤压过程中均析出棒状W相和α-Mn相,且均匀分布于Mg基体中。在325℃挤压的GEZM8181合金综合性能最佳,其屈服强度、抗拉强度和伸长率分别为326 MPa、352 MPa和17.1%,热导率达到140 W/(m·K)。GEZM8181合金力学性能的提升主要归因于晶粒细化和析出强化,而热导率的增加则主要是由于大量W相和α-Mn相的析出净化了Mg基体。本研究表明,通过优化挤压工艺来调控微观组织,可实现镁合金型材力学性能和导热性能的协同提升。     

稀土元素对Al-Si-Cu合金导电导热性能的影响

铝合金作为市场上应用最广泛的散热器制造材料之一,其导电导热性能与该行业未来的发展密切相关。本文以Al-Si-Cu压铸铝合金体系中的ADC12合金作为研究对象,采用正交实验法向合金中添加不同含量的La、Ce、Er三种稀土元素,研究各稀土元素含量对合金的显微组织、硬度及导电导热性能的影响。结果表明：添加稀土金属元素会使合金中的Si相和α-Al基体产生不同程度的细化,并且能在一定程度上提高合金的硬度及导电导热性能。当稀土添加量为0.04%La、0.06%Ce、0.13%Er时,观察到合金的显微组织排列最规整,电导率从原来的24.84%IACS提升到了32.93%IACS,而热导率也从96.69W/（m·K）提升到了119.53 W/（m·K）,合金的导电导热性能都得到了较大的提升。     

变形对Al-Zn-Mg-Cu合金时效析出相的影响

通过球差校正透射电镜,对相同时效处理工艺下,变形与未变形的Al-Zn-Mg-Cu合金样品中的纳米析出相进行了形貌、尺寸的统计分析和结构的原子分辨率表征,分析了变形对Al-Zn-Mg-Cu合金时效析出相演变的影响。结果表明：变形影响后续时效过程中析出相的形貌,使得板条析出相的数量下降,圆形析出相的数量上升。此外,板条析出相的尺寸倾向于在厚度方向增加,长度方向减小。变形导致析出相结构改变,形成多块非连续的局域性的纳米畴。这可能是由于位错切割析出相后析出相部分溶解,继续时效时不同区域生长速率和生长方向改变导致的。     

热处理对Fe13Cr5Al1.5Nb合金晶粒尺寸及第二相析出行为的影响

利用光学显微镜、透射电镜、扫描电镜以及电子背散射衍射研究了Fe13Cr5Al1.5Nb合金的高温下微观组织演化特征。选择模拟事故工况温度区间(800～1000℃)对合金进行热处理实验,研究热处理温度和时间对晶粒尺寸及第二相析出行为的影响规律。采用EBSD分析统计了晶粒尺寸的变化。研究了800℃×20 h热处理后材料在室温至800℃的拉伸性能并观察分析了拉伸断口特征。结果表明,冷轧/热轧合金中弥散分布着高温稳定性良好的细小析出相(Fe2Nb相),且其周围分布着高密度位错。在800℃热处理5～25 h过程中,FeCrAl基合金的晶粒尺寸保持了良好的热稳定性,合金的晶粒尺寸都比较细小,平均晶粒尺寸约2μm。高于900℃时,合金中大量第二相固溶于基体,部分第二相显著粗化。低于260℃时,断口形貌表现为微孔型塑性断裂,呈现典型的细小蜂窝状等轴韧窝;提高到600～800℃时,合金出现超塑性特点。     

喷射沉积制备7055合金冷却过程对第二相析出的影响

通过分级保温工艺,对喷射沉积制备7055合金冷却过程进行了研究。采用XRD、SEM、TEM等手段,研究了7055合金中第二相的析出情况。结果表明,经NaOH萃取,发现存在η-MgZn₂、S-Al₂CuMg、T-Al₂Mg₃Zn₃相。7055铝合金经325℃×30min的保温最接近喷射沉积的冷却过程,析出了细小的η-MgZn₂相,细长的S-Al₂CuMg相以及片状T-Al₂Mg₃Zn₃平衡相。通过模拟冷却研究逆推,合金在凝固过程中析出了第二相,这些第二相在冷却过程中长大成为微米级的第二相（η-MgZn₂相）,而细小η-MgZn₂相,细长S-Al₂CuMg相,片状T-Al₂Mg₃Zn₃相等纳米级的第二相,主要是在冷却过程中析出。     

石墨烯对6063铝合金铸锭导热性能的影响

采用混粉球磨、压制预制块及熔融铸造的方法制备出高导热的石墨烯/6063铝基复合材料铸锭。利用扫描电镜、火花直读光谱仪、X射线衍射以及拉曼光谱仪表征复合材料的成分含量、微观结构与缺陷等,并且分析了石墨烯的加入对于复合材料的导电、导热性能的影响。结果表明,制备的石墨烯/铝基复合材料且石墨烯在铝基体中分布较均匀。添加0.5%的石墨烯对于复合材料的导电、导热性能提升明显,其热导率提升到226.11 W/(m·K),电导率提升到32.34 MS/m,相比未添加石墨烯的热导率增幅为16.0%,电导率提高了3.93%。     

合金元素对SKD61钢中析出相热力学的影响

采用Thermo-calc热力学计算软件,对SKD61钢在400～1600℃存在的平衡相进行了热力学计算,探讨了不同合金元素含量对回火析出相析出行为的影响,在此基础上设计出热处理工艺,并对热处理试样中的析出相经电解腐蚀后进行扫描电镜(SEM)和EDS研究。计算结果表明:SKD61钢中平衡析出相主要为MC、M7C3、M6C和M23C6,试样回火后的稳定析出相为MC和M23C6,合金元素V、C对MC相和M23C6相影响最大。SKD61钢热处理后的结果显示,该模具钢较合适的淬火温度区间为(1040±20)℃,回火温度的确定应以不出现粗大的M23C6碳化物相为宜。     

热处理对ATX525镁合金中CaMgSn相形貌演化的影响

采用XRD、SEM和EDS研究了热处理温度对ATX525镁合金相组成、显微组织和析出相成分的影响,考察了保温时间为24 h条件下,Ca Mg Sn相随温度变化的演化规律。结果表明,合金组织中析出相由热稳定性较高的Mg2(Al,Ca)、Al2Ca和Ca Mg Sn等相组成。其中,Ca Mg Sn相中Sn和Ca含量随处理温度变化而变化,从而使其热稳定性和形貌发生变化。当温度低于500℃时,主要发生Ca Mg Sn溶断和破碎过程,体积分数没有显著变化;当温度为550℃时,Ca Mg Sn相发生溶入基体过程,体积分数减少;然而当处理温度为570~600℃,Ca Mg Sn相出现长大现象。获得细化Ca Mg Sn相貌的热处理温度为500~550℃。合金经过550℃/24 h处理后,经200℃/96 h时效,Ca Mg Sn相以条状和细小的颗粒状析出,与颗粒形貌相比,条状Ca Mg Sn相具有铸态时的形貌特征。     

压铸Al-Zn-Si-Cu合金的力学与导热性能

采用压铸工艺制备了Al-xZn-8Si-2Cu(x=12、14、16、18,/%)合金型材。使用OM、SEM分析Zn含量对合金微观组织形貌的影响,并进一步分析Zn含量对力学性能及导热性能的影响。结果表明,当合金中Zn含量从12%提升到18%时,固溶在α-Al基体中的Zn含量提高,对合金起到固溶强化作用,同时共晶Si尺寸增大形成尖角导致应力集中;合金的抗拉强度和屈服强度分别从345.5 MPa、263.5 MPa提高到395.4 MPa、343.8 MPa;伸长率略微降低;热导率由109.4 W/(m·K)降低到85.7 W/(m·K)。     

Mg-Al-Zn系镁合金在大气中的散热性能研究

在20~220℃范围内对比研究了AZ80、AZ31、ZK60镁合金和AA6082铝合金在大气中的散热性能,分别测量其环境散热曲线并用指数型热动力学方程T=T_0+ΔT_0·exp(-t/A_0)拟合。结果表明,固溶处理可使铸态或挤压态镁合金热导率下降,而固溶+时效处理后其热导率有所提升。分析了瞬时温差与瞬时温度比值ΔT/T与镁合金、铝合金散热性能的关系,自然对流条件下,柱高对AZ80镁合金散热性能影响较小;在人工强制对流条件下,当0.25ΔT/T0.45时,高柱(60 mm)散热速率约为低柱(20 mm)的两倍。在自然对流条件下,AZ80、AZ31镁合金的散热性能在0.25ΔT/T0.45(120~220℃)时,明显优于AA6082铝合金。在0.05ΔT/T0.25(20~120℃)时,这3种合金的散热性能无明显差别。     

Effect of intermetallics on susceptibility of Mg alloy welds to liquation cracking

ABSTRACT

The circular-patch welding test was used to study the liquation and liquation cracking of AZ-series Mg alloys. A heat treatment was carried out on the as-received AZ91 alloy to dissolve the γ(Mg₁₇Al₁₂) particles before welding. The circular-patch welding test was then conducted on the heat-treated, as-received AZ91 alloy using AZ61 and AZ91 filler wires. The results showed that the susceptibility of AZ91 alloy to liquation and liquation cracking was significantly reduced by the dissolution of massive γ(Mg₁₇Al₁₂) particles via a heat treatment before welding as the liquation mechanism was changed. Both constitutional liquation and incipient melting occurred in the partially melted zone of the as-received AZ91 welds, while only incipient melting occurred in the heat-treated AZ91 welds.     

Heat transfer during quenching of modified and unmodified gravity die-cast A357 cylindrical bars

Heat transfer during quenching of chill-cast modified and unmodified A357 Al-Si alloy was examined using a computer-aided cooling curve analysis. Water at 60 °C and a vegetable oil (palm oil) were used as quench media. The measured temperatures inside cylindrical probes of the A357 alloy were used as inputs in an inverse heat-conduction model to estimate heat flux transients at the probe/quenchant interface and the surface temperature of the probe in contact with the quench medium. It was observed that modified alloy probes yielded higher cooling rates and heat flux transients. The investigation clearly showed that the heat transfer during quenching depends on the casting history. The increase in the cooling rate and peak heat flux was attributed to the increase in the thermal conductivity of the material on modification melt treatment owing to the change in silicon morphology. Fine and fibrous silicon particles in modified A357 probes increase the conductance of the probe resulting in higher heat transfer rates. This was confirmed by measuring the electrical conductivity of modified samples, which were found to be higher than those of unmodified samples. The ultrasound velocity in the probes decreased on modification.     

A novel white afterglow phosphorescent phosphor Ca3SnSi2O9: Dy

AZ91 alloy powder with 2 mass% Si addition (flakes) was obtained by two-roller quenching equipment with an atomized accessory. The powders were consolidated and extruded into bar. The microstructures of the powders (flakes) and bars were characterized by optical microscope (OM), XRD, TEM and SEM. The results showed that the grain size of the powder were dendritic with the sizes of about 1–5 μm. The as-extruded alloy bars retain equiaxed grains with a large number of precipitated phases, i.e. Mg₂Si, β-Al₁₂Mg₁₇ and AlMg₂Zn. The alloy exhibits excellent mechanical properties. The 0.2% yield tensile strength, ultimate tensile strength and elongation of rupture were 322.47, 429.78 MPa and 6.4%, respectively. The as-extruded alloy bars show preferable elevated temperature mechanical properties.     

Effect of heat treatment on the thermal conductivity of plasma-sprayed thermal barrier coatings

The effect of heat treatment on the thermal conductivity of plasma-sprayed Y₂O₃ stabilized ZrO₂ (YSZ) and Al₂O₃ coatings was investigated. A heat treatment of 1300 °C in flowing argon for 50 h was found to significantly increase the thermal conductivity of the coatings when compared to measurements in the assprayed condition. Transmission electron microscopy (TEM) examination of the microstructures of the coatings in the as-sprayed and heat-treated conditions revealed that sintering of microcracks at the splat interfaces was the main cause for the increase in thermal conductivity. In the YSZ coatings, complete closure of microcracks was frequently observed. In contrast, microcrack closure in the Al₂O₃ coatings was characterized by the isolated necking of particles across a microcrack rather than complete closure. A model for thermal conductivity in a solid containing oriented penny-shaped cracks was used to explain the observed increase in thermal conductivity after heat treatment.     

镁及其合金表面处理研究现状

镁及其合金由于具有优良的性能而得到了广泛应用,但由于该合金非常活跃,很容易被腐蚀,而使其应用也受到了限制,因此可以通过适当的表面处理方法来改善镁合金的耐腐蚀性能.较系统地综述了镁合金表面处理的研究现状,介绍了以电镀和化学镀为主要内容的金属镀层处理,以普通阳极氧化和微弧氧化为主要内容的阳极氧化法以及化学转化法和高能束技术在镁合金表面处理中的应用.经这些方法处理后镁合金的耐蚀性得到了明显提高.     

7075和2024铝合金的固溶组织与力学性能

研究了升温固溶处理对提高7075和2024铝合金的结晶相固溶程度和力学性能的影响。升温固溶可使最终固溶温度超过多相共晶温度而不产生过烧组织,提高结晶相固溶程度。7075合金的结晶相较2024合金的易于固溶。两种合金的力学性能与固溶程度密切相关。强化固溶的7075合金强度提高约20%,断裂和屈服强度可达660 MPa和606 MPa,其性能提高的幅度大于强化固溶的2024合金。     

镁合金的表面处理及其发展趋势

综述了镁合金的化学转化膜,阳极氧化,微弧氧化以及化学镀等表面处理方法,总结了镁合金防护中的发展趋势。