The solubility of hydrogen in solid binary aluminum-lithium alloys
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log ( S / S ~ - 2 log (p/pO) = T/-----K+ B where S, S o are, respectively, the of diatomic hydrogen P, p0 are, respectively, the Pa (1 atm). The values of the constants A and
solubility and a standard value of solubility equal to 1 cm 3 measured at 273 K and 101,325 Pa/100 g of metal; pressure and a standard value of pressure equal to 101,325 B are
AI-1 pct Li 473 < T / K < 680: 680 < T / K < 873:
A = 358; A =604;
B =0.576 B =0.620
A1-2 pct Li 473 < T / K < 740: 740 < T / K < 873:
A =273; A=676;
B=0.597 B =0.767
A1-3 pct Li 523 < T / K < 770: 770 < T / K < 873:
A =615; A=830;
B = 1.272 B = 1.166
The solubility of hydrogen is one or two orders of magnitude greater in the alloys than in the pure metal and increases with lithium content. The results are consistent with the dissociative dissolution of a diatomic gas. The isobars are discontinuous at critical temperatures which lie within the a-phase field, i.e., 680, 740, and 770 K for AI-1 pct Li, A1-2 pct Li, and A1-3 pct Li, respectively, indicating a change in the character of the solution at lower temperatures due to an increase in the solute binding energy, which is attributed provisionally to an unidentified change in the ~ matrix.
I.
INTRODUCTION
W H E N liquid aluminum or any of its alloys is cast by the techniques used in normal production routes, it retains virtually all of the dissolved hydrogen it may contain; but if the hydrogen content exceeds a relatively low threshold value, some of the gas is rejected from the solution and is trapped within the solidifying structure, generating interdendritic porosity, which reduces the quality and yield of subsequent wrought products, m The sensitivity of aluminum and its alloys to unsoundness is due primarily to the low solubility of hydrogen in the solid metal I2-3l and the associated low partition coefficient for hydrogen between the solid and liquid fractions present as the metal solidifies, m Alloys containing lithium differ radically from established alloys in their response to dissolved hydrogen. The incidence of interdendritic porosity in ingots of these alP.N. ANYALEBECHI, formerly with the Department of Materials Technology at Brunel, The University of West London, United Kingdom, is Research Engineer with the ALCOA Technical Center. D.E.J, TALBOT, Senior Lecturer, is with the Department of Materials Technology at Brunel, The University of West London, Uxbridge, Middlesex UB8 3PH, United Kingdom. D.A. GRANGER, Research Fellow, is with the ALCOA Technical Center, Aluminum Company of America, Alcoa Center, PA 15069. Manuscript submitted August 8, 1988. METALLURGICAL TRANSACTIONS B
loys is much lower than for other alloys, even though standard industrial degassing procedures are less effective in removing hydrogen from the liquid metal from which they are cast. The original purpose of the present work was to produce values for the solubility of hydrogen in solid binary alloys for comparison with published values for liquid alloys with the same compositions I4j and, hence, to assess whether t
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