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Al–Ag–Mg Aluminum–Silver–Magnesium system
423
Al-Ag-Li Aluminum-Silver-Lithium system There is a compound, AgLi2Al (72.5% Ag; 9.4% Li): f.c.c; space group F43m; 16 atoms to the unit cell; parameter a = 6.35 xlO" 10 m; density 3 860kg/m3 [ 1 ]. Whether this compound is in equilibrium with aluminum or not was not ascertained. REFERENCE 1. H. Pauly, etc., MeM 1, 120413
Al-Ag-Mg Aluminum-Silver-Magnesium system The solid solubility of magnesium in aluminum is reduced by silver additions [1—3b] and there is a ternary compound with a composition within the formula (AgAl)49Mg32 (67.3% Ag, 19.1% Mg at Ag^A^MgaJ [3-5], isomorphous with (ZnAl)49Mg32 and CuMg4Al6, most probably with a wide range of existence. It is b.c.c; space group lm3\ 162 atoms to the unit cell; parameter a= 14.5xl0" 10 m [3b, 4]. Another compound with the formula AgMgAl (68% Ag, 15.1% Mg) is formed by peritectic reaction, liq. + A g M g ^AgMgAl+ A1, at 843°K [6, 7]. AgMgAl is a Laves phase; hexagonal; space group Ρβ^/mmc; 12 atoms to the unit cell; parameters a = 5.39 x 10- 10 m, c=8.73 x 10 -10 m [3b, 7]. A quasibinary section, Al-AgMgAl, is reported by [6], but denied by [7]. The solid solubility of AgMgAl on the quasibinary line decreases from 14% AgMgAl at 820 °K to 1% at 600 °K [6]. Aluminum is in equilibrium also with AgMg, which can dissolve some aluminum, possibly to a formula MgAg2Al (81% Ag, 9% Mg) [3b, 7]. AgMg (18.2% Mg) is b.c.c; space group Pm3m; 2 atoms to the unit cell; lattice parameter a = 3.31 xl0~ 1 0 m [8]. Figure 3.2 shows the phase distribution in the solid state at 775 and 475 °K [3b]. Properties of the aluminum-magnesium alloys with small additions of silver do not differ substantially from those of the binary alloys, but the corrosion resistance is radically reduced [6, 9, 10]. According to [11], addition of 0.3% Ag to a 11% Mg alloy increases the strength some 10%, without loss of corrosion resistance. In the age hardening of aluminum-silver alloys the magnesium tends to concentrate in the GP zones, but does not affect the precipitation of Ag2Al [12]. In the age hardening of the alloys on the AgMg-Al line no GP zones were detected and the following orientation relationship was determined: (100) AgMg |(211) AI ;
[211]
AgMg I [no]
Al
At the lower aging temperatures Ag2Al precipitates together with AgMg; at the higher temperatures the ternary compound can be detected [7]. In the alloys with Mg : Ag ratios between approximately 2:1 and 5:1 the precipitate is (AgAl)49Mg32; with higher ratios Mg5Al8. When (AgAl)49Mg32 is the precipitate, aging starts with the formation of more or less spherical zones, with a tetragonal lattice, space group Pm3m. As the zones grow, the parameters shift from
424
Wt.%Ag
Figure 3.2. Aluminum corner of the aluminum-silver-magnesium diagram. Solid lines, phase distribution at 800 °K; dashed lines, phase distribution at 500 °K. T = (AgAl)49Mgn phase
a = 4.37xlO- 10 m, c = 4.05 x\0~ 10m at the beginning to a = 4.42x10" 10 m, c= 3.48 x 10~10m at the end. The orientation relationship of the zones is [3, 5] (100)GP||(110)A1;
[OIOIGPIIIOOUAI
At higher temperatures the zones are replaced by (AgAl)49Mg32, with the orientation relationship (100)T|(112)A1;
[OOUTIUÏOIAI
Above 500 °K no zones are formed [5]. When Mg5Al8 is the main precipitate (Mg:Ag>5), the structural features are the same as in the binary aluminum-magnesium alloys, but the presence of silver accelerates the process and tends to produce a finer β' phase. Hardening is faster and more pronounced [3, 13, 14]. The precipitate-free zone at grain boundaries may be reduced by silver additions [14-15], provided that the proper heat treatment practice is used [16]. REFERENCES 1. 2. 3. 3b. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 14b. 15. 16.
M. I. Zamotorin, Tr. Leningrad Politekhn. Inst., 1959, (202), 25 I. N. Fridlyander, etc., Deformimenuye Alyumin Splavy, Sb. Statei, 1961 T. Ito, etc., Met A 3, 110393, 140219; 5, 140659 B. E. Williams, Met A 6, 110376 M. J. Wheeler, etc., MA 1, 641 J. H. Auld, Met A 1, 140126 B. Otani, JIM 53, 548 K. Kusumoto, etc., JIMMA 25, 915 Pearson, 2 W. Kroll, JIM 37, 454; 39, 484 T. Endo, etc., Met A 3, 312311 M. F. Komarova, etc., Met A 1, 120659 R. R. Zakharova, etc., JIMMA 29, 340 F. J. Kievits, etc., MA 1, 351; Met A 1, 140242 M. F. Komarov, etc., MA 1, 1679; Met A 1, 140054 Y. Baba, Met A 6, 140223, 140291 E. A. Starke, Jr., Met A 3, 140487 B. S. Subramanya, Met A 1, 140293
Al-Ag-Li Aluminum-Silver-Lithium system There is a compound, AgLi2Al (72.5% Ag; 9.4% Li): f.c.c; space group F43m; 16 atoms to the unit cell; parameter a = 6.35 xlO" 10 m; density 3 860kg/m3 [ 1 ]. Whether this compound is in equilibrium with aluminum or not was not ascertained. REFERENCE 1. H. Pauly, etc., MeM 1, 120413
Al-Ag-Mg Aluminum-Silver-Magnesium system The solid solubility of magnesium in aluminum is reduced by silver additions [1—3b] and there is a ternary compound with a composition within the formula (AgAl)49Mg32 (67.3% Ag, 19.1% Mg at Ag^A^MgaJ [3-5], isomorphous with (ZnAl)49Mg32 and CuMg4Al6, most probably with a wide range of existence. It is b.c.c; space group lm3\ 162 atoms to the unit cell; parameter a= 14.5xl0" 10 m [3b, 4]. Another compound with the formula AgMgAl (68% Ag, 15.1% Mg) is formed by peritectic reaction, liq. + A g M g ^AgMgAl+ A1, at 843°K [6, 7]. AgMgAl is a Laves phase; hexagonal; space group Ρβ^/mmc; 12 atoms to the unit cell; parameters a = 5.39 x 10- 10 m, c=8.73 x 10 -10 m [3b, 7]. A quasibinary section, Al-AgMgAl, is reported by [6], but denied by [7]. The solid solubility of AgMgAl on the quasibinary line decreases from 14% AgMgAl at 820 °K to 1% at 600 °K [6]. Aluminum is in equilibrium also with AgMg, which can dissolve some aluminum, possibly to a formula MgAg2Al (81% Ag, 9% Mg) [3b, 7]. AgMg (18.2% Mg) is b.c.c; space group Pm3m; 2 atoms to the unit cell; lattice parameter a = 3.31 xl0~ 1 0 m [8]. Figure 3.2 shows the phase distribution in the solid state at 775 and 475 °K [3b]. Properties of the aluminum-magnesium alloys with small additions of silver do not differ substantially from those of the binary alloys, but the corrosion resistance is radically reduced [6, 9, 10]. According to [11], addition of 0.3% Ag to a 11% Mg alloy increases the strength some 10%, without loss of corrosion resistance. In the age hardening of aluminum-silver alloys the magnesium tends to concentrate in the GP zones, but does not affect the precipitation of Ag2Al [12]. In the age hardening of the alloys on the AgMg-Al line no GP zones were detected and the following orientation relationship was determined: (100) AgMg |(211) AI ;
[211]
AgMg I [no]
Al
At the lower aging temperatures Ag2Al precipitates together with AgMg; at the higher temperatures the ternary compound can be detected [7]. In the alloys with Mg : Ag ratios between approximately 2:1 and 5:1 the precipitate is (AgAl)49Mg32; with higher ratios Mg5Al8. When (AgAl)49Mg32 is the precipitate, aging starts with the formation of more or less spherical zones, with a tetragonal lattice, space group Pm3m. As the zones grow, the parameters shift from
424
Wt.%Ag
Figure 3.2. Aluminum corner of the aluminum-silver-magnesium diagram. Solid lines, phase distribution at 800 °K; dashed lines, phase distribution at 500 °K. T = (AgAl)49Mgn phase
a = 4.37xlO- 10 m, c = 4.05 x\0~ 10m at the beginning to a = 4.42x10" 10 m, c= 3.48 x 10~10m at the end. The orientation relationship of the zones is [3, 5] (100)GP||(110)A1;
[OIOIGPIIIOOUAI
At higher temperatures the zones are replaced by (AgAl)49Mg32, with the orientation relationship (100)T|(112)A1;
[OOUTIUÏOIAI
Above 500 °K no zones are formed [5]. When Mg5Al8 is the main precipitate (Mg:Ag>5), the structural features are the same as in the binary aluminum-magnesium alloys, but the presence of silver accelerates the process and tends to produce a finer β' phase. Hardening is faster and more pronounced [3, 13, 14]. The precipitate-free zone at grain boundaries may be reduced by silver additions [14-15], provided that the proper heat treatment practice is used [16]. REFERENCES 1. 2. 3. 3b. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 14b. 15. 16.
M. I. Zamotorin, Tr. Leningrad Politekhn. Inst., 1959, (202), 25 I. N. Fridlyander, etc., Deformimenuye Alyumin Splavy, Sb. Statei, 1961 T. Ito, etc., Met A 3, 110393, 140219; 5, 140659 B. E. Williams, Met A 6, 110376 M. J. Wheeler, etc., MA 1, 641 J. H. Auld, Met A 1, 140126 B. Otani, JIM 53, 548 K. Kusumoto, etc., JIMMA 25, 915 Pearson, 2 W. Kroll, JIM 37, 454; 39, 484 T. Endo, etc., Met A 3, 312311 M. F. Komarova, etc., Met A 1, 120659 R. R. Zakharova, etc., JIMMA 29, 340 F. J. Kievits, etc., MA 1, 351; Met A 1, 140242 M. F. Komarov, etc., MA 1, 1679; Met A 1, 140054 Y. Baba, Met A 6, 140223, 140291 E. A. Starke, Jr., Met A 3, 140487 B. S. Subramanya, Met A 1, 140293