Effect of Buffer Layer Type on the Mechanical Properties and Corrosion Resistance of Magnetron Sputtered Cr Coatings on 7050 Al Alloy

Limited hardness and corrosion resistance restrict 7050 aluminum alloys in aggressive environments. Cr coatings, applied as single layers or over Ti, Al, or Ni buffer layers, were deposited onto 7050 aluminum alloy by direct-current magnetron sputtering; their microstructure, adhesion, mechanical properties, and corrosion behavior were examined. The results indicate that introducing a buffer layer significantly enhances the bonding strength between a Cr coating and an aluminum alloy substrate, with the Ni buffer layer exhibiting the highest bonding strength, nearly three times that of the Cr coating alone. Furthermore, the buffer layer influences the mechanical properties of the Cr coatings, with Ni/Cr and Al/Cr coatings demonstrating increased hardness and elastic modulus. The Ni/Cr coating achieved the highest values of 3.95 GPa and 62.09 GPa, respectively. Regarding corrosion performance, The Cr coatings containing buffer layers showed markedly better corrosion resistance than the bare 7050 Al alloy. A compact Cr2O3 passive film formed on their surfaces, cutting the corrosion current density by roughly two orders of magnitude. Among all samples, the Ti/Cr coating performed best, registering the lowest current density (1.687 × 10−6 A cm−2) and the highest charge-transfer resistance (6090 Ω cm2).