铝合金压铸用模具钢表面的渗铝氧化处理

对8407模具钢试样进行热浸渗铝,在试样表面形成了Fe-Al合金渗层.对渗铝试样进行高温氧化实验,使渗层表面形成了Fe-Al-O的混合氧化物.考察了渗铝温度和渗铝时间对渗层质量的影响;着重研究了不同氧化气氛下Fe-Al合金表面的氧化情况,确定了最佳高温氧化工艺.结果表明,8407钢热浸镀铝后,在600 ℃以下、纯O2气氛条件下氧化,Fe-Al合金表面生成了Fe3O4和Al2O的混合物.这层氧化膜与铝液不润湿,能较好地保护试样.因此这种工艺可能是合适的铝合金压铸模表面处理工艺.     

8407钢渗铝氧化处理形成的氧化膜组织与结构

对渗铝后的8407钢试样进行常温硬质阳极氧化处理,使其表面形成氧化膜。通过金相显微镜观察氧化膜横截面组织,并探讨了氧化膜的形成机制;采用扫描电镜观察氧化膜表面形貌,并检测氧化膜沿厚度方向的化学成分及其分布;利用X射线衍射仪对氧化膜相组成进行分析。结果表明,渗铝8407钢经过常温硬质阳极氧化后,试样表面分为3层,从基体向外侧依次为基体、渗层、氧化膜。氧化膜连续致密,厚度均匀,与基体结合紧密,其主要成分为O、Al和Fe,且各元素分布均匀,主要相组成为Fe3O4和Al2O3。     

纯铜表面催渗渗铝及弥散强化研究

提出了用稀土合金CeCl3进行催渗的纯铜渗铝技术。采用渗铝—内氧化技术制备了Al2O3表面弥散铜基导电材料。研究了CeCl3合金催渗对渗铝层的影响和表面弥散层的显微组织及有关性能。结果表明:利用稀土合金CeCl3催渗的纯铜渗铝试样渗层厚度远高于同等工艺参数下未催渗的纯铜渗铝试样。内氧化后,能在渗铝层形成Al2O3弥散硬化层。     

渗铝钢在卤水中的腐蚀行为研究

对Q235钢经过固体包埋渗铝后,观察渗层组织,并对渗层进行XRD衍射分析以及EDS能谱分析,并将渗铝钢浸泡于盐溶液中进行电化学测试以及观察腐蚀产物。结果表明:Q235钢经过高温固体包埋渗铝后形成的渗层致密连续,渗铝层组织主要为针状组织,Fe元素和Al元素是碳钢渗铝后渗层的主要元素,渗铝层主要由Fe2Al5、Al Cl3和Al2O3组成;Q235钢经过腐蚀后,表面的腐蚀产物疏松且容易脱落,碳钢表面渗铝后,在腐蚀环境中,表面生成的腐蚀产物不容易脱落且致密完整,钢基体能够受到表面腐蚀产物较好的保护;电化学试验表明,碳钢渗铝后在盐溶液中抵抗腐蚀的能力明显好于未渗铝钢。     

稀土对45钢硼铝共渗渗层生长初期的影响

本文研究了稀土对45钢硼铝共渗层生长初期的影响,建立了渗层生核长大模型。试验结果表明:稀土硼铝共渗试样在保温8分钟时表面就已形成较完整渗层,而硼铝共渗试样表面则24分钟才完成这一过程。由此认为,稀土促进了渗剂的分解,并促使活性元素大量吸附在试样表面,提高了硼化物的成核速度和成核率。     

8407模具钢表面渗铝后的常温硬质阳极氧化

为了防止模具钢表面产生热熔损失效,对渗铝后的8407钢表面进行常温硬质阳极氧化实验,使试样表面形成了氧化膜.着重研究了电流密度和氧化时间对氧化膜厚度和硬度的影响.实验结果确定适宜的氧化条件是:电流密度为2.5 A/dm2左右,氧化时间在60 min左右,氧化温度在25 ℃左右.     

铜合金表面渗铝工艺研究

利用粉末包埋法对低铝铜合金表面进行渗铝,考察不同的密封性、温度、时间对渗铝层的影响,结果表明:用管式容器在900 ～950℃进行渗铝,保温6～8h,可以获得170 ～200 μm左右的渗铝层.经SEM观察,发现渗铝层厚度非常均匀,与基体有明显的界面,界面结合良好,渗层组织较基体致密.利用阿累尼乌斯经验公式求得铝的扩散激活能为103.69 kJ/mol.     

沉淀硬化不锈钢机械能助渗铝的试验研究

通过机械能助渗铝工艺,实现对沉淀硬化不锈钢的低温渗铝.500℃渗铝10 h,可以在保证基体材料的力学性能基本无损耗的情况下,得到厚度约为11μm的均一渗铝层.采用SEM、EDS、显微硬度分析以及盐雾试验等测试手段对渗铝层进行研究,发现通过机械能助渗铝得到的为富铝相渗层,渗层硬度是基体材料的两倍以上,且具有良好的耐腐蚀及...     

AZ91D镁合金表面电弧喷涂/微弧氧化复合陶瓷涂层结构组成与耐蚀性研究

通过一种新的电弧喷涂/微弧氧化(EASP/MAO)复合工艺,在AZ91D镁合金表面制备了复合陶瓷涂层。电弧喷涂处理试样在430℃下进行了热扩散处理后,在以硅酸盐碱性电解液体系中进行微弧氧化处理。利用扫描电镜(SEM)、能谱分析仪(EDS)和X射线衍射仪(XRD)对复合涂层表面和截面形貌、元素和相组成进行了分析,利用CS2350双单元电化学工作站对涂层试样在3.5%NaCl溶液中的动电位极化曲线进行了测定。结果表明:在430℃、氩气保护氛围下,保温热扩散处理2 h后,在基材与喷涂铝层间形成了热扩散层,扩散层由Al3Mg2和Al12Mg17两相组成。由于电弧喷涂铝涂层存在较多的表面缺陷,其对AZ91D镁合金基材只能起到有限的保护作用。经微弧氧化处理后,电弧喷涂铝涂层表面形成氧化铝陶瓷层,主要由α-Al2O3和γ-Al2O3两相组成。跟AZ91D镁合金基体相比,经微弧氧化处理10,20 min后的试样在3.5%NaCl溶液中的自腐蚀电位分别正移到-0.8279,-1.0570 V,较基体约分别提高770,550 mV,腐蚀倾向降低,基体的自腐蚀电流密度为经过微弧氧化处理10 min后试样的4.1倍,为经过微弧氧化处理20 min试样的460.6倍。     

辉光放电光谱仪逐层分析Cr12钢表面渗硼层

采用两种不同的工艺在Cr12钢表面制备渗硼层,利用辉光放电光谱仪对两种工艺形成的Cr12表面渗硼层进行逐层分析。结果表明:1#试样(1000℃处理10h)渗硼层在距表面0～20μm内均由质量分数为8.8%的硼组成,随后硼的含量逐渐降低;2#试样(900℃处理10h)渗硼层的硼含量在表面较低,随后逐渐升高到质量分数为5%左右,接着又缓慢降低。由此推测1#试样的表面可能存在Fe2B;2#试样的表面可能由硼在铁中的α固溶体组成。为了验证辉光放电光谱仪逐层分析渗硼层的可靠性,利用XRD分析了渗硼层的相结构,结果表     

304不锈钢表面冷喷涂TC4钛合金涂层性能研究

采用冷喷涂技术在304不锈钢表面制备了TC4钛合金涂层,通过扫描电子显微镜观察了涂层的形貌、组织结构,并利用电化学方法研究了涂层的腐蚀电化学特征。研究结果表明,冷喷涂制备的TC4钛合金涂层致密性存在较为明显的梯度现象,靠近基体的涂层密度明显高于表面;涂层喷涂过程没有出现明显氧化现象,与基体的结合强度可达20 MPa左右;涂层的耐腐蚀性能优于304不锈钢,可大大提升不锈钢材料在海洋环境中的耐点蚀性能。     

The Effectiveness of Surface Coatings on Preventing Interfacial Reaction During Ultrasonic Welding of Aluminum to Magnesium

High power ultrasonic spot welding (USW) is a solid-state joining process that is advantageous for welding difficult dissimilar material couples, like magnesium to aluminum. USW is also a useful technique for testing methods of controlling interfacial reaction in welding as the interface is not greatly displaced by the process. However, the high strain rate deformation in USW has been found to accelerate intermetallic compound (IMC) formation and a thick Al₁₂Mg₁₇ and Al₃Mg₂ reaction layer forms after relatively short welding times. In this work, we have investigated the potential of two approaches for reducing the IMC reaction rate in dissimilar Al-Mg ultrasonic welds, both involving coatings on the Mg sheet surface to (i) separate the join line from the weld interface, using a 100-μm-thick Al cold spray coating, and (ii) provide a diffusion barrier layer, using a thin manganese physical vapor deposition (PVD) coating. Both methods were found to reduce the level of reaction and increase the failure energy of the welds, but their effectiveness was limited due to issues with coating attachment and survivability during the welding cycle. The effect of the coatings on the joint’s interface microstructure, and the fracture behavior have been investigated in detail. Kinetic modeling has been used to show that the benefit of the cold spray coating can be attributed to the reaction rate reverting to that expected under static conditions. This reduces the IMC growth rate by over 50 pct because at the weld line, the high strain rate dynamic deformation in USW normally enhances diffusion through the IMC layer. In comparison, the thin PVD barrier coating was found to rapidly break up early in USW and become dispersed throughout the deformation layer reducing its effectiveness.     

State‐of‐the‐Knowledge on Coating Systems for Hot Stamped Parts

In the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe–Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zn‐induced embrittlement are analyzed. The use of Zn–Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol–gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al–Zn alloy coatings, dual layer Zn–Al and Zn–Al–Mg coatings is also introduced. The application of Zn–Al–Mg post‐process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.     

Fracture Behavior of Cold Sprayed 304 Stainless Steel Coating During Cold Rolling

 The fracture behavior of cold sprayed 304 stainless steel coating in cold rolling process was studied. The 304 stainless steel coatings were deposited on low carbon steel substrate by cold gas dynamic spray (CGDS) and then cold rolled, respectively. The fracture morphology of the coatings was observed and analyzed, and the crack distributions along the longitudinal rolling direction of the coatings were also investigated and discussed. The results showed that the cohesive strength of the cold sprayed 304 stainless steel coating was too low to be cold rolled. Microcracks were formed in the as-sprayed coatings and ran perpendicularly to the rolling direction. The spacing distance between these cracks decreased with the increase of the cold rolling reduction. In addition, it was also found that the initial crack generated at the surface of the coating and propagated from the surface to the interface along the weakly bonded particles. A theoretical analysis was developed for the coating fracture. It gave a critical minimum cohesive bonding strength of the coating for non-breaking in cold rolling process. The crack propagation manner of the cold rolled coatings was also discussed.     

Electrochemical Behavior and Microstructure of Recyclable Aluminium-magmesium Alloy Hot-dip Coating Deposited on Low Carbon Steel Substrates

With the abundance and good corrosion resistance of aluminium, hot-dip technique was used to prepare the recycled Al with 8.2 mass% Mg alloy coating on low carbon steel substrates. Electrochemical behavior of this coating was investigated by anodic polarization and open circuit potential measurement. Its microstructure and composition were observed by scanning electron microscope and energy-dispersive X-ray spectrometry, respectively. The long lasting corrosion performance of coated steels was investigated under the salt fog spray test. From anodic polarization curves and open circuit potential, recycled Al with 8.2 mass% Mg coating performed adequate sacrificial ability. At 0.40 V, current density of recycled Al with 8.2 mass% Mg alloy coating was about 200 000 times higher than that of pure recycled Al coating, and was about 0.5 times lower than that of Zn coating. The microstructure of recycled Al with 8.2 mass% Mg alloy coating on the steel substrate consisted of Al3Mg2, Al-Fe intermetallic compound and Al matrix. The results from salt fog spray test showed that recycled Al with 8.2 mass% Mg alloy coated steel had similar corrosion resistance ability to Zn coated steel.     

高铝双相钢氧化特性规律

采用酸洗、冷轧以及高温氧化模拟试验等分析方法,对高铝双相钢的热卷表面铁皮特点以及生长规律进行分析。结果表明,高铝双相钢热轧板表面易于形成鱼鳞状红铁皮缺陷,冷轧后表面容易产生色差形貌,影响表面质量;由于钢中铝元素添加较多,铁皮的界面可捕捉到明显的铝元素富集形貌,在1300℃模拟试样的铁皮界面Al2O3形成黑色颗粒带,颗粒带内铝质量分数最高可达18%以上;铁皮内的铝元素富集情况随着温度的降低逐渐下降,作用层厚度减薄;基于对高铝钢铁皮形成的机理分析提出降低出炉温度、适当降低过程温度等手段来控制鱼鳞状铁皮形成。     

Ce对热浸镀铝HP40Nb钢氧化行为及组织的影响研究

通过SEM,EDS和XRD研究了Ce对HP40Nb热浸镀铝层组织结构和高温抗氧化性能的影响.结果表明,热浸镀过程中添加质量分数1％Ce促进了镀层外层中Fe2Al5和Fe4Al3Ce相的生成,抑制了内层Fe2Al5相长大;在1 000 ℃/4 h扩散处理过程中,Ce促进了γ向α相的转变以及α相中Ni3Al相的析出,并在渗层内层中生成富Ce相;800C/360 h氧化后,Ce促使渗层外层生成少量Fe2Al5和Cr3Si相,并使渗层外层组织均匀致密;1000℃/360 h氧化后,Ce促使α相长大导致渗层中生成大量的σ相.800℃氧化实验发现1％Ce使渗层组织致密,提高了渗层高温抗氧化性;1 000℃氧化实验发现1％Ce促进了渗层中σ相的生成,阻碍了Al原子的内扩散,保证了氧化过程中渗层表面生成α - Al2O3所需铝含量.     

低压冷喷涂铸造缺陷修复涂层性能研究

低压冷喷涂(LPCS)是一种拥有便携式冷喷涂系统的涂层技术。例如DYMET304K系统就应用于这项涂层技术中。通常情况下,压缩空气作为冷喷涂工艺中的运载气体。低压冷喷涂适用于喷涂金属基陶瓷复合粉末,如Cu基、Ni基、Zn基、Al基添加Al2O3粉的复合粉。硬质陶瓷相主要起到清洁喷嘴、增加表面活性和喷丸强化的作用,该方法在尺寸修复领域中具有优势。在这个领域里,修复铸造加工中的缺陷和气孔是一个很热门的应用。例如,Zn基复合材料就适用于防止电化学腐蚀和修复机械损伤造成的尺寸差异。本文对Zn+Al+Al2O3,Zn+Cu+Al2O3和Zn+Ni+Al2O3等复合材料做了实验研究。Zn和Al在腐蚀环境中起到阴极保护的作用,而Cu和Ni也有助于提高材料的机械性能。经过对微观孔蚀电位反应和力学性能(硬度和结合强度)的研究发现,涂层具有相对致密的结构和耐蚀性能。Zn在复合涂层中对其它金属起到阴极保护的作用。此外,在Fe52型铁基材料上的涂层有着足够的力学性能,硬度和结合强度较高。这一类涂层在修复宏观的铸造缺陷上具有很高的潜在应用价值。     

制备工艺方法对 NiCrFeMo 涂层组织和性能影响研究

采用等离子喷涂、 超音速火焰喷涂和冷喷涂工艺制备了 NiCrFeMo 涂层, 并对涂层的金相性能、 不同基体 材料下涂层的结合性能、 不同温度下涂层的耐磨性能进行了检测。 实验结果表明： 采用冷喷涂工艺制备的涂层孔 隙率最低, 对应涂层的结合强度最高, 但冷喷涂工艺制备的涂层对基体材料较为敏感, 而超音速火焰喷涂和等离 子喷涂受基体材料影响不大。 在室温下, 冷喷涂涂层显示出较优的耐磨性能, 在高温下超音速火焰喷涂涂层显示 出较优的耐磨性能。     

铝镁及稀土铝镁电弧喷涂涂层的耐腐蚀性能研究

采用电弧喷涂技术在Q235钢表面制备了Al-Mg和Re-Al-Mg涂层,分别研究了这两种涂层的耐腐蚀性能,利用中性盐雾试验及电化学测试等试验方法研究了两种涂层的防腐蚀性能并通过扫描电子显微镜分析了Al-Mg和Re-Al-Mg涂层腐蚀前后的微观组织形貌,并讨论了涂层的结构及耐蚀机理,结果表明两种涂层在极化过程中都出现了明显的钝化现象,两种涂层在腐蚀过程中表面都会生成一层氧化膜,起到了物理屏蔽作用延缓了涂层的腐蚀速率,但稀土铝镁合金涂层的防腐蚀性能明显优于铝镁合金涂层,这是由于稀土元素的加入,降低了涂层的孔隙率,使涂层具有了良好的耐腐蚀性能。稀土铝镁合金涂层在中性盐雾试验中表现出的腐蚀速率是最慢的,电化学试验过程中其表现出钝化区域最大,具有良好的腐蚀与防护性能。