Suppression of Samson phase formation in Al-Mg alloys by boron addition

Abstract

Al-Mg alloys, particularly Al 5083 and Al 5456, are widely used for boat and ship structural applications because of their unique properties such as lightweight, high strength and good weldability. However, structural parts manufactured with these alloys fail catastrophically as a result of the formation of Al 3 Mg 2 , known as Samson phase, at grain boundaries. Here we demonstrate that the Samson phase formation is suppressed in Al 5083 by alloying with B, which traps most of Mg in solid solution as AlMgB 2 phase. This decreases the supersaturation level of Mg in Al matrix, which is a driving force for the formation of Samson phase in Al 5083. We observe Cu-rich precipitates, instead of the Samson phase, at grain boundaries upon extended annealing at 150C. This is a significant finding as it provides new insight as to how to minimize the longstanding problem of sensitization.

Mechanical properties, corrosion behavior, and microstructure of Sr modified Al–9.2Mg–0.7Mn alloys

“…Gupta et al indicated strontium to be the most effective addition in decreasing β phase fraction during thermal exposure by calculation. However, Goswami et al also clearly pointed out in their paper that Sr, Nd, and Zn cannot effectively inhabit the formation of β phase on the grain boundary, and reported for the first time that B and Cu were added to Al 5083 alloys to restrain the formation of Samson phase (Al 3 Mg 2 ) effectively. This was achieved by the formation of a new ternary phase (AlMgB 2 ) which decreased the supersaturation level of Mg in Al matrix.…”

Improving strength and corrosion resistance of high Mg alloyed Al–Mg–Mn alloys through Ce addition

“…However, it is unclear whether the Al 20 Mn 2 Ce phase is quasi-crystal or that it does not exist in the present study due to limitations in the cooling rate and temperature excursion [34]. Another plausible explanation is that Ce-rich compounds are formed on pre-existing Al 6 Mn particles in the Al matrix due to the nucleation effect of the Mn-rich phase [7,19,25]. A certain amount of fine Ce-rich particles disperse in the grain interiors and at the grain boundaries, which possibly obstructs grain growth during heat treatment by hindering grain boundary migration and provides a certain amount of precipitation hardening.…”

“…In recent years, various strategies have been developed to improve the properties of Al-Mg alloys with an Mg content lower than 5% (such as the development of Al5083). These strategies include adjusted processing technologies [9][10][11][12][13] and micro-alloying [14][15][16][17][18][19][20][21]. In the case of micro-alloying, Mn, Zr [14], Yb, and Sc [15,16] are believed to improve the mechanical properties of Al-Mg alloys without any deterioration in their corrosion performance.…”

“…It has been reported that the addition of Zn to Al5083 results in the formation of Mg 32 (Al, Zn) 49 along the grain boundaries [17,18], thus dramatically decreasing the difference in the electrode potential of certain phases [18]. In the case of B micro-alloying, a new AlMgB 2 phase is formed and hence reduces the supersaturation level of Mg in the α-Al matrix, the latter of which is the driving force for the formation of the β phase [19]. Gupta et al recently found that Nd addition is highly effective in improving the sensitization resistance of an Al-5Mg model alloy [22], and determined that Sr addition can reduce the IGC sensitivity of Al5083 alloys, using theoretical calculations [23].…”

Enhancing the intergranular corrosion resistance of high Mg‐alloyed Al–Mg alloy by Y addition

“…[ 15 ] The B addition in Al5083 would bring about the formation of a new AlMgB 2 phase and, hence, decrease the supersaturation level of Mg in α‐Al, which is a driving force for the formation of β‐Al 3 Mg 2 . [ 16 ] A recent study has found that a minor Nd addition is highly effective in improving the sensitization resistance of the Al–5Mg alloy. [ 17 ] In our previous study, a minor Sr addition (in the form of the Mg–Sr master alloy) in the as‐cast Al–9.2Mg–0.7Mn alloy brings about a new (Al, Mg) 17 Sr 2 phase, resulting in the improved IGC resistance after the sensitization treatment.…”