A survey of some metallographic etching reagents for restoration of obliterated engraved marks on aluminium–silicon alloy surfaces

Metallographic Etching of Aluminium and Its Alloys for Restoration of Obliterated Marks in Forensic Science Practice and Investigations

“…However, when the marks were erased by grinding and a new number was engraved in their place, the recoverable depth decreased to 0.02 mm (Izhar et al, 2008). Similar effects were observed with the other two Al alloys (Bong & Kuppuswamy, 2010;Uli et al, 2010) and also with steel surfaces (Azlan et al, 2007). The results only indicated that the deformation zone from the original engraving was not affected by the new overengraving up to certain levels, but beyond this depth the original deformation was lost.…”

“…In cases of engraved marks on steel and aluminium surfaces the depths of recoverable deformations varied between 2 and 3 times the depths of engraving (Azlan et al, 2007;Izhar et al 2008;Bong & Kuppuswamy, 2010;Uli et al, 2010). In cases of marks produced by pin stamping and engraving the depth of plastic deformation or strain is not as great as in stamping.…”

“…The present author along with Izhar and Rahman (Izhar et al, 2008), Bong (Bong & Kuppuswamy, 2010), and Norjaidi and Firdaus (Uli et al, 2010) reviewed the sensitivity and efficacy of some common etchants on Al (99% purity), Al-Zn-Mg-Cu and Al-Si alloys. High strength Al-Zn-Mg-Cu alloy finds applications in automobile components and frames of firearms, while Al-Si alloy is used as motor vehicle engines.…”

“…Among the eight common metallographic reagents tested, reagents 4 to 8 (in Table 2) did not give the desired contrast and sensitivity (see for details Izhar et al, 2008;Bong & Kuppuswamy, 2010;& Uli et al, 2010) and hence were not suitable. The reagents 1 to 3 produced superior results both in terms of contrast and sensitivity for etching specific aluminium surfaces.…”

“…While NaOH etching restored the marks, the rinsing with HNO 3 removed the black deposit (Mondolfo, 1943;Petzow, 1976) caused by NaOH swabbing thereby increasing contrast. (For details see Uli et al, 2010). Interestingly, HumeRothery reagent recommended for etching Al-Si alloy surfaces in metallurgical literature (Mondolfo, 1943;Vander Voort, 1984) could not restore the obliterated marks.…”