Surface Coating from Phosphonate Ionic Liquid Electrolyte for the Enhancement of the Tribological Performance of Magnesium Alloy

Abstract

A chronoamperometric method has been applied for the growth of a surface coating on AZ31B magnesium alloy, using the imidazolium alkylphosphonate room-temperature ionic liquid 1-ethyl-3-methylimidazolium ethylphosphonate ([EMIM][EtPO3H]) as electrolyte. A surface coating layer is obtained after 4 h under a constant voltage bias of -0.8 V with respect to the standard electrode. The coating nucleation and growth process correlates well with a 3D progressive mechanism. X-ray photoelectron spectrometry (XPS) analysis of [EMIM][EtPO3H] shows new P 2p and O 1s peaks after its use as electrolyte, as a consequence of reaction between the phosphonate anion and the magnesium substrate. Angle-resolved XPS (ARXPS) analysis of [EMIM][EtPO3H] did not show any change in the composition of the surface before and after chronoamperometry, since the sampling depth (1.5 nm at the highest emission angle) is larger than the cation and anion sizes (ca. 7 and 5 Å, respectively). Characterization of the coating was made by scanning electron microscopy (SEM), focussed ion beam SEM, energy dispersive X-ray spectroscopy, XPS, and ARXPS. FIB-SEM shows that the coating presents a mean thickness of 374 (±36) nm and contains magnesium and aluminum phosphates. Linear reciprocating tribological tests under variable load show that the presence of the coating can reduce friction coefficients of the coated AZ31B against steel up to 32% and wear rates up to 90%, with respect to the uncoated alloy.

Synergistic Effect of MoS2 and SiO2 Nanoparticles as Lubricant Additives for Magnesium Alloy–Steel Contacts

“…Controlling friction by lubrication is important in metal forming not only for reducing energy consumption but also for enhancing the surface quality of the formed components and the forming limitations [ 10 ]. Nonetheless, so far few lubricants are exclusively used for the forming process of Mg alloy, and in some cases, the forming lubricants used for Al alloy forming are casually used and the consequences are not favorable.…”

Electrochemical treatment of aluminium alloy 7075 in aqueous solutions of imidazolium phosphonate and phosphate ionic liquids and scratch resistance of the resultant materials

“…Recently [7][8][9], the formation of surface films on magnesium alloy by treatment with ionic liquids (ILs) containing P has been studied. Although initial studies confirmed improvement in the corrosion resistance of magnesium alloys due to the formation of a passivating surface film when immersion in phosphonium IL, this surface film used to be heterogeneous and with defects [9].…”

New Alkylether–Thiazolium Room-Temperature Ionic Liquid Lubricants: Surface Interactions and Tribological Performance

“…In the field of surface science and engineering, ionic liquids have shown outstanding potential as lubricants and lubricant additives [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] , even in the friction and wear reduction of highly reactive light alloys [17][18][19][20] , polymers [21][22][23][24][25][26] , and also as nanophase modifiers 23,24 , electrolytes [27][28][29] , corrosion inhibitors [27][28][29][30][31][32][33][34][35][36] or promoters of surface coatings [37][38][39][40] .…”