Revealing obliterated engraved marks on high strength aluminium alloy (AA7010) surfaces by etching technique

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

“…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.…”

“…The reagents 1 to 3 produced superior results both in terms of contrast and sensitivity for etching specific aluminium surfaces. The reagent 1, 60% HCl and 40% NaOH on alternate application on aluminium (99% purity) (Izhar et al, 2008) and Al-Zn-Mg-Cu alloy surfaces (Bong & Kuppuswamy, 2010) were quite successful for recovering the marks obliterated by erasure, overengraving and peening. These are seen in Figs.…”

“…A specific percentage of each of these on alternate swabbing produced the desired results. For Al-Zn-Mg-Cu alloys (Bong & Kuppuswamy, 2010) another application, 10 % aq. phosphoric acid by immersion for extended hours recovered the marks with excellent contrast.…”