Effect of Al coating conditions on laser weldability of Al coated steel sheet

Al coated steel sheets with excellent heat resistance,thermal reflection,and corrosion resistance are widely used in various applications.The laser weldability of the Al coated steel sheet for full penetration welding was reported.The phenomenon caused by intermixed aluminum and behavior of aluminum in the weld were investigated.Al coated steel sheets that have various thickness and coating mass were prepared for laser welding.The effects of parameters such as welding conditions and Al coating conditions were investigated.Al content mixed in the weld after laser welding was evaluated,and then a correlation between the mixed Al and mechanical properties was investigated.The results show that the Al-rich zones which have Fe-Al intermetallic compounds are found in the weld.The intermetallic compounds cause the decreased strength of the weld.

The development of advanced Cr-free organic composite coated electrogalvanized steel sheet with excellent grounding property

In recent years,the concern about environmental protection is increasing on a world scale.Major manufacturers of home appliances and OA equipment have introduced so-called 'green procurement schemes' for reducing environmentally harmful substances in manufacturing process and end products. Under such background,a new type of chromate-free organic composite coated electro-galvanized steel sheet with high conductivity was developed by Baosteel,which meets the EU RoHS Directive(Restriction of the Hazardous Substances) and other related laws and regulations on environmental safety.It also provides excellent surface electrical conductivity,corrosion resistance,fingerprint resistance,solvent resistance,coating adhesion, heat resistance,formability and other special properties to meet the demand of manufacture's process of OA machine. Compared with previously developed anti-fingerprinting coated electro-galvanized steel sheet,this newly developed product has a good balance between high corrosion resistance(time to 5%white rust in salt spray test is 120 h for flat panel and 72 h for worked potion) and conductivity(surface electro-resistivity in accordance with LOREAST is less than 0.1 milliohm ) due to the special design of coating's structure.Besides,It also provides the properties of grounding and shielding against electromagnetic waves.The evaluation of surface performances of new product showed that it is comparable or even better than the similar products. Currently,the newly developed product has been commercialized. In this paper,the major properties are discussed,such as corrosion resistance,surface electrical conductivity, fingerprint resistance,solvent resistance,coating adhesion(ink/melamine alkyd paint),heat resistance and formability.Furthermore,the application is also briefly described.

AN EXPERIMENTAL STUDY OF CO_2 LASER CUTTING OF METALLIC COATED SHEET STEELS

An experimental investigation is outlined for the CO 2 laser cutting process of metallic coated sheet steels, GALVABOND. It shows that by proper control of the cutting parameters, good quality cuts are possible at high cutting rate. Visual examination indicates that when increasing the cutting rate to as high as 5000 mm/min (about 100 times that suggested previously), kerfs of better quality can be achieved. Some kerf characteristics such as the width, heat affected zone and dross in terms of the process parameters are also discussed. A statistical analysis has arrived at a recommendatio on the optimum cutting parameters forprocessing GALVABOND.

Self-cleaning performance of a self-cleaning pre-coated steel sheet in an industrial environment

A type of self-cleaning pre-coated steel sheet with excellent self-cleaning performance was developed using hydrophilic surface treatment technology. To understand the self-cleaning properties of this pre-coated steel sheet in an industrial environment, the Jiangjin natural environmental test station was chosen as the outdoor exposure test to be conducted, and the self-cleaning performance of the steel sheet was studied by measuring the water contact angle, stain resistance factor, color difference, and gloss of the steel sheet during the outdoor exposure test. The water contact angle of the self-cleaning steel sheet quickly decreased from 84° to 29° during the outdoor exposure test, and the steel sheet showed excellent hydrophilic properties, which were beneficial to the spread of rain drops and detrimental to the accumulation of the surface pollutants. After an outdoor exposure of 12 months,the self-cleaning steel sheet had a higher stain resistance and cleaner surface than the comparison sample sheet, demonstrating its excellent self-cleaning properties. Moreover, the color difference and gloss rate of the self-cleaning steel ＇sheet were similar to those of the pre-coated steel sheet without hydrophilic surface treatment. Therefore, the hydrophilic surface treatment technology used in this study did not affect the anti-aging property of the self-cleaning steel sheet.

Experimental and finite element analysis for fracture of coating layer of galvannealed steel sheet

Mechanical properties of galvannealed (GA) steel sheet used for automotive exposed panel and predicted failure phenomenon of its coating layer were evaluated using finite element method. V-bending test was performed to understand better the fracture of coating layer of GA steel sheet during plastic deformation. Yield strength of the coating layer was calculated by using a relative difference between hardness of coating layer measured from the nano-indentation test and that of substrate. To measure shearing strength at the interface between substrate and coating layer, shearing test with two specimens attached by an adhesive was carried out. Using the mechanical properties measured, a series of finite element analyses coupled with a failure model was performed. Results reveal that the fracture of coating layer occurs in an irregular manner at the region where compressive deformation is dominant. Meanwhile, a series of vertical cracks perpendicular to material surface are observed at the tensile stressed-region. It is found that 0.26-0.28 of local equivalent plastic strain exists at the coating and substrate at the beginning of failure. The fracture of coating layer depends on ductility of the coating layer considerably as well.

Research on the lack of alloying in the galvannealed coating of automotive sheet steel

Samples of the cross section microstructures of galvannealed steel sheets that lack alloying were analyzed. X-ray diffraction （XRD） tests were carried out. The study discovers that the deficit of alloying was higher on both sides of the steel sheet when compared to the center and the thickness of the coating on the sides was also higher than the center. The results of the XRD tests demonstrate that the microstructure of the coating with a lack of alloy is mainly composed of zinc,ζ and δ. They also indicate that the lack of alloying is mainly due to a lower galvannealing temperature and thicker coating. It is shown by the optical micrographs of coating that the δ phase forms first in a discontinuous manner at the interface and then rapidly pushes towards the coating and enlarges.

Study on the formation of intermetallic phases in the new type of Zn-Mg coatings on steel sheets

Zn-Mg alloy coatings were obtained by physical vapor deposition （PVD） on electroplated steel sheets. Study on the formation of intermetallic phases in the coatings was conducted through the use of X-ray diffraction （XRD） ,scanning electron microscope （SEM） and glow discharge optical emission spectrometry （GDOES）. It is found that MgZn2 is the main Zn-Mg alloy phase formed after heat treatment. The formation of Mg-Zn intermetallic phases is controlled not only by thermodynamics, but also by kinetics. MgZn2 has different morphologies, such as laminar structure,porous structure and floc-like structure,which are mainly determined by the annealing temperature. Obvious diffusion of Mg starts at 350 ℃, and the diffusion of iron increases significantly when the temperature is elevated to 380℃.

Effect of surface roughness on the surface lubrication performance of galvanized steel sheets with a self-lubricated coating

Four kinds of galvanized steel sheets having different surface roughness values were used to prepare the steel sheets with a self-lubricated coating. The effects of surface roughness on the surface lubrication performance of the steel sheets were examined using a friction coefficient tester. Results revealed large dynamic friction coefficients for the galvanized steel sheets, which increased remarkably with surface roughness. Once the self-lubricated coating was applied, significant drops in the dynamic friction coefficients were measured. After the first stage of the friction test,the coefficients were almost unchanged, which reflected a weak dependence on the surface roughness of the self-lubricated steel sheets. However, the dynamic friction coefficients gradually increased as the test progressed, where these increase clearly correlated with the surface roughness of the self-lubricated steel sheets.

Characteristics and application of Baosteel's Cr-free ultrathick J coat for non-oriented silicon steel sheets

Baosteel＇ s Cr-free ultrathick J coat for non-oriented silicon steel sheets has excellent insulation performance and has been successfully applied to middle and large scale electric power trains and wind electric power devices, which have stricter requirements than typical for coat insulation. In this paper, the characteristics and application of this type of coating for non-oriented silicon steel sheets were described in detail.

Evolution of appearance profile of hot-dip galvanized car-body steel sheet during deformation process

In recent years, the waterborne free intermediate coating process has been widely used in the automotive industry. Because the baking times and coating thickness are decreased, the surface covering capability of the painting process is reduced, which directly affects the appearance quality（ long-and short-wave values） of the body paint. Thus, there are correspondingly higher requirements for the white body surface profile prior to painting. The surface profile of the white body is mainly affected by the plate material, the surface profile, and the deformation process. So,the change rule for the surface profile during deformation of the steel plate is a key factor in coating appearance optimization. In this paper, we first analyze the typical deformation of the outer cover of a car body. Then ,we examine the change tendency of the surface profile of steel plates with respect to different deformation rates, specifically for a steel plate comprising a hot-dip galvanized bake-hardened steel sheet. Based on our analysis of the influence of the deformation on the coating appearance,we selected 3% ,5% ,and 8% deformation rates in this research. We found the roughness （Ra） value in the typical deformation range （3% -8% ） of the car body to exhibit a decreasing trend at first and then an increasing trend. The Ra value of the 8% deformation is not more than the original plate test value. When the Pc value of the original plate is in the lower range （ about 60）, it exhibits a slight increasing trend in the deformation process （3 % -8 % ）. And when the Pc value of the original plate is in the higher range （ about 120 ）, it exhibits no increasing trend in the deformation process （ 3% -8% ）. In contrast,the waviness （WCA） value in the car body＇s typical deformation range （3%-8%） shows a significant growth trend.

脱脂碱度对镀锌板涂装前处理性能的影响

[目的]脱脂过程中,镀锌板镀层表面与OH−发生反应导致材料表面状态变化,从而影响材料的涂装性能。[方法]使用扫描电镜、电化学工作站、X射线荧光光谱仪等设备研究了不同脱脂碱度下镀锌板脱脂性能、磷化性能、锆化性能及电化学性能。[结果]脱脂pH分别为10.5、11.5和12.5时,3种镀锌板的脱脂性能和磷化性能无明显差异。随着脱脂pH由10.5升至12.5时,镀锌板的锆化性能获得提升,锆化膜重呈上升趋势,而且镀锌板的腐蚀电流密度增大13%~47%,电荷转移电阻降低16%~50%。[结论]随着脱脂碱度升高,镀锌板表面的Al及氧化物溶解程度增大,其表面活性点增多,锆化反应的阻力降低。通过控制脱脂碱度可有效调整镀锌板的锆化性能。

中铝锌铝镁无铬自润滑产品的表面特性

[目的]中铝锌铝镁钢板亟需一款适合微电机使用场景的自润滑膜层。[方法]通过对中铝锌铝镁表面3种无铬自润滑产品的表面微观形貌及膜层成分进行探究,分析了不同表面处理方式的各项性能,并结合自润滑产品的组成特性及实际使用场景,考察了不同自润滑膜层的耐蚀性、耐磨性等关键性能,明晰了造成各项性能差异的原因。[结果]与1#及2#有机弱酸性体系无铬自润滑产品相比,3#有机-无机复合自润滑膜层是偏无机酸性体系,与钢板表面的界面反应更强,具有较好的附着力,耐蚀性、耐指纹性、导电性、耐磨性等性能也更优。[结论]3#无铬自润滑产品膜层中的磷酸根为腐蚀抑制剂,磷酸盐又是隔离层与粘结层的有效成分,可进一步提高膜层的抗腐蚀能力。氟钛酸作为该涂层的润滑添加剂,不仅充当了提高润滑涂层耐蚀性的缓蚀剂,还充当了填充剂,填充于膜层孔隙中,有利于致密自润滑膜的形成,有效地减小了摩擦因数,提高了成型性能。

不同类型铝硅镀层热成型钢的耐蚀性研究

[目的]铝硅镀层热成型钢的镀层厚度对其防腐性能影响较大,有必要对汽车上使用的铝硅镀层热成型常规镀层板(镀层厚度20~33μm)、薄镀层板(镀层厚度6~14μm)及变厚度板的耐蚀性进行比较。[方法]采用中性盐雾(NSS)试验对热成型前后试样的耐蚀性进行考察。[结果]热成型前,常规镀层板在NSS试验1109 h时才出现红锈,薄镀层板在283 h后便出现红锈,变厚度板薄区618 h后出现红锈;热成型及电泳后,常规镀层板和薄厚度板的单边扩蚀宽度分别为0 mm和4.0 mm,变厚度板上基板厚度为2.3、2.0和1.8 mm的区域的单边扩蚀宽度分别为0.5、2.0和2.0 mm。[结论]热成型前,铝硅镀层板的耐蚀性与镀层的表面层隔离作用有关;热成型及电泳后,镀层的扩散层厚度对腐蚀的影响较大,变厚度板的防腐性能较薄镀层板好,但比常规镀层板差。

汽车车身常用板材耐腐蚀性能研究

车身常用板材的耐腐蚀性能是车身板材选用的重要参考标准,因此,对已加工为零件的热浸镀铝硅镀层板、未加工为零件的热浸镀铝硅镀层板、电镀锌板、热镀锌板、热成型钢裸板和冷轧板分别进行裸板材板和电泳板的中性盐雾对比试验。结果表明:有镀层的板材耐腐蚀性能明显优于无镀层板材;热浸镀铝硅镀层板加工成零件后其镀层会被破坏,导致其裸板耐腐蚀性能下降,但其电泳板的耐腐蚀性能加工前后变化不大,划痕扩蚀情况反而提升;热成型钢裸板因加工过程形成的氧化膜和脱碳层,在中性盐雾条件下4 h即出现锈蚀,其电泳板和电泳划痕板中性盐雾试验均出现严重的起泡问题。

热浸镀锌铝镁镀层钢板硅烷涂装性能评价

以热浸镀纯Zn镀层板为对比,对具有不同表面状态(涂油或钝化)的热浸镀锌铝镁(ZM)镀层平板及双拉变形板在汽车主机厂进行了硅烷电泳处理,随后对其硅烷膜和电泳漆膜的品质进行了评价。结果表明:ZM镀层板的硅烷涂装性能优于纯Zn镀层板;变形对纯Zn镀层和ZM镀层的涂装性能无明显影响,但表面钝化会明显降低电泳漆膜的附着力和耐蚀性。

全无铬钝化镀锌板成形后的耐腐蚀性能

采用扫描电镜(SEM)和辉光放电光谱仪(GDS)研究了变形量对全无铬钝化镀锌板表面形貌和元素分布的影响。通过电化学分析、中性盐雾试验、循环盐雾试验和硫酸铜点滴试验,对比了不同变形量时全无铬钝化板的耐蚀性。结果表明,当主应变增大到3%时,钝化膜表面开始出现裂纹;随着主应变的继续增大,裂纹尺寸逐渐加大,裂纹主要出现在光整坑内部。随变形量增大,全无铬钝化板的耐蚀性变差。

碱洗除油对热镀锌钢涂装后耐蚀性的影响

对比研究了有机溶剂除油和碱洗除油镀锌板的表面微观结构和成分,磷化膜性能,以及电泳漆膜耐蚀性。结果表明,采用碱洗除油时,镀锌板电泳涂装后的抗石击腐蚀性能明显优于采用有机溶剂除油时。

热镀锌及锌铝镁合金钢在不同大气环境下的腐蚀行为

选用热镀锌(GI)钢和热镀锌铝镁合金(ZM)钢,分别在吐鲁番、江津、青岛和万宁4种典型环境地区中进行大气腐蚀试验。通过分析镀层腐蚀后的形貌、微观组织结构和腐蚀产物成分,探究了纯Zn镀层和Zn–Al–Mg合金镀层在不同大气环境下的腐蚀行为。结果表明,在相同大气环境下服役时,ZM具有比GI更优异的耐蚀性。两者在干燥大气中的腐蚀速率都较低,在潮湿工业大气环境和近海高氯大气环境中的腐蚀速率较高,腐蚀产物以Zn(OH)_(2)、ZnO、ZnCO_(3)及Zn5(CO_(3))_(2)(OH)_(6)为主。

POZD涂覆钢板加固钢筋混凝土板抗爆性能研究

为了研究聚异氰氨酸酯噁唑烷(Polyisocyanate oxazodone,POZD)聚合物高分子材料涂覆钢板-钢筋混凝土板在接触爆炸荷载作用下的抗爆性能,开展了接触爆炸试验和数值模拟研究,对其破坏特征进行分析。采用有限元软件LS-DYNA建立了钢筋混凝土板、炸药、钢板和POZD的有限元模型,讨论了不同药量下POZD涂覆钢板加固钢筋混凝土板的破坏模式和破坏特征。试验及数值结果表明:在钢板-钢筋混凝土板背面涂覆POZD涂层能有效提升结构的抗爆性能;在接触爆炸作用下,POZD涂覆钢板加固钢筋混凝土板试件呈现四种破坏模式。

不同光整工艺对全无铬钝化热镀锌板耐蚀性的影响

分别采用普通磨辊和超精细磨辊对热镀锌板进行光整处理得到不同微观形貌的表面,再进行全无铬钝化处理。对比了采用不同光整工艺时所得全无铬钝化膜的表面形貌和元素分布。通过电化学测试和循环盐雾试验探究了采用不同光整工艺时镀锌板表面无铬钝化膜的耐腐蚀性能。结果表明,超精细磨辊处理后全无铬钝化热镀锌板表面更平坦,钝化膜覆盖更均匀,表面活性位点少,耐腐蚀性能更好。