The use of aluminium alloys as the material of manufacturing has increased tremendously such as manufacturing of Nissan, Audi, Honda and BMW cars. However, there is lack of complete data on the best technique for restoration of obliterated serial numbers on such alloy used in the engine block. This research study was carried out to identify the most efficient and sensitive reagent among the five different etchants for restoration of obliterated markings on aluminium alloy surfaces. The aluminium alloy engine block of Nissan car was cut into small plates, and each plate was engraved with some alphanumerical characters using a computer-controlled “Gravograph” machine. Then, the marks were erased using abrasive papers to different levels (0.03 mm, 0.05 mm, 0.08 mm and 0.1 mm), below the bottom part of the engraving marks. The erased plates were etched by swabbing or immersion in each tested reagent. Etching with etchant that contained 10 g NaOH and 90 mL of water was useful to reveal the obliterated marks. Marks that were removed from 0.03 to 0.1 mm below the bottom of engraving were successfully restored with good contrast and in less time (minimum time of 23 min). Another reagent 10% aq. H₃PO₄ was also effective to restore the obliterated marks when the erased areas were immersed in it for long hours (minimum time of 21 h). On the other hand, reagent of 10% NaOH and 10% NHO₃ had also achieved fair contrast and reproducible restoration of marks from 0.03 to 0.1 mm below the depth of engraving. All the restored alphanumerical characters on the plates were visualised using fluorescent powder irradiated with UV light. In contrast, other two tested reagents, i.e. 60% HCl and 40% NaOH, 1 N NaOH and 0.1 M HgCl₂ in 0.1 N HCI, showed poor contrast restoration and hence were not recommended for practical application. The findings from this research would help the investigator particularly in stolen car cases to choose the best etching reagent for restoration of obliterated serial numbers as well as to improve etching procedures on the aluminium alloy surfaces used in the car engines.

铝合金作为制造材料的用途已大大增加，例如日产，奥迪，本田和宝马汽车的制造。但是，关于在发动机缸体中使用的这种合金上恢复ob刻的序列号的最佳技术，尚缺乏完整的数据。进行了这项研究，以找出五种不同蚀刻剂中最有效，最灵敏的试剂，用于修复铝合金表面上的划痕。将日产汽车的铝合金发动机缸体切成小块，然后使用计算机控制的“ Gravograph”机器在每块板上刻上一些字母数字字符。然后，使用砂纸在雕刻标记底部下方将其擦除至不同水平（0.03毫米，0.05毫米，0.08毫米和0.1毫米）。通过擦拭或浸入每种被测试剂中来蚀刻擦除的板。用含有10克NaOH和90毫升水的蚀刻剂蚀刻可以显露出被遮盖的痕迹。从雕刻底部下方0.03到0.1毫米处去除的标记可以以良好的对比度和更少的时间（最少23分钟）成功恢复。另一试剂10％水溶液 H₃ PO ₄在擦除区域长时间浸泡（最少21小时）时也可以有效恢复遮盖的痕迹。另一方面，10％NaOH和10％NHO _3的试剂也获得了相当的对比度，并且在雕刻深度以下0.03至0.1 mm处可再现地恢复了标记。使用紫外光照射的荧光粉使板上恢复的所有字母数字字符可视化。相反，其他两种测试试剂，即60％HCl和40％NaOH，1 N NaOH和0.1 M HgCl ₂在0.1 N HCl中显示的对比度恢复较差，因此不建议在实际应用中使用。这项研究的发现将有助于研究人员，特别是在被盗汽车箱中，选择最佳的蚀刻剂来恢复被遗忘的序列号，以及改善在汽车发动机中使用的铝合金表面上的蚀刻程序。