Purpose

This paper aims to overcome the corrosion in AA7075 by incorporating the dual-reinforcements like Al2O3 and SiC through friction stir processing (FSP). In recent days, an automotive monocoque structure undergoes corrosion because of changes in environmental conditions.

Design/methodology/approach

Surface hybrid composites (SHCs) of AA7075 with different weight ratios of Al₂O₃ and SiC were fabricated at a rotating speed of 1000 rpm, traveling speed of 56 mm/min and tool tilt angle of 2º with two passes. Surface regions were observed using optical microscopy, and the potentiodynamic corrosion test was performed under a 3.5 per cent NaCl environment at room temperature. Then, the surface morphology analysis of corroded samples and their structural properties were also investigated through scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron dispersive spectroscopy (EDS).

Findings

Through FSP, an improved interface between the reinforced particles and the AA7075 base matrix was observed because of the severe plastic deformation. Potentiodynamic polarization tests confirmed that the AA7075 matrix with a higher concentration of Al₂O₃ and a lower concentration of SiC (Al₂O₃ – 75 per cent and SiC – 25 per cent) possesses a lower corrosion rate than other specimens. This result is because of the combined effect of stable passive film formation and the resistance produced by hard SiC particles. In addition, the formation of a stronger interface between the reinforcements and the base matrix impedes the NaCl solution attack. The SEM micrograph depicts the film crystallinity variations with an increase in Al₂O₃ content. Debonding between the layers was observed on increasing the SiC content in the base matrix. XRD shows the peaks of reinforcing elements that influence the corrosion behavior. These observations suggest that the AA7075 reinforced with a higher concentration of Al₂O₃ and a lower concentration of SiC through FSP affords a suitable solution for automotive monocoque applications.

Originality/value

The corrosion rate has been identified for AA7075 SHCs with various concentrations of Al₂O₃ and SiC and has been compared with that of the base metal and the friction stir processed specimen without reinforcement.

中文翻译：

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通过搅拌摩擦加工定制的AA7075表面杂化复合材料的腐蚀行为研究

目的

本文旨在通过摩擦搅拌工艺（FSP）结合Al2O3和SiC等双重增强材料来克服AA7075中的腐蚀。近年来，由于环境条件的变化，汽车单体结构受到腐蚀。

设计/方法/方法

分两次通过，以1000 rpm的转速，56 mm / min的行进速度和2º的工具倾斜角制造了具有不同重量比的Al ₂ O ₃和SiC的AA7075表面杂化复合材料（SHC）。使用光学显微镜观察表面区域，并在室温下在3.5％NaCl环境下进行电位动力学腐蚀试验。然后，还通过扫描电子显微镜（SEM），X射线衍射（XRD）和电子分散光谱（EDS）研究了腐蚀样品的表面形态分析及其结构性质。

发现

通过FSP，由于严重的塑性变形，观察到了增强颗粒和AA7075基体之间的界面改善。动电位极化测试证实有Al的浓度高的AA7075矩阵₂ ö ₃和SiC较低浓度（铝₂ ö ₃ - 75％和SiC - 25％）具有较低的腐蚀速率比其它试样。该结果是由于稳定的钝化膜形成和硬质SiC颗粒产生的电阻共同作用的结果。另外，在增强物和基础基质之间形成更强的界面会阻碍NaCl溶液的侵蚀。SEM显微照片描述了膜结晶度随Al的增加而变化₂ O ₃含量。在增加基础基质中的SiC含量时，观察到层之间的剥离。XRD显示了影响腐蚀行为的增强元素的峰。这些观察结果表明，通过FSP用较高浓度的Al ₂ O ₃和较低浓度的SiC增强的AA7075提供了适用于汽车整车应用的解决方案。

创意/价值

已确定了具有不同浓度的Al ₂ O ₃和SiC的AA7075 SHC的腐蚀速率，并已与未增强的贱金属和摩擦搅拌处理的试样进行了比较。