In-situ analysis of continuous cooling precipitation in Al alloys by wide-angle X-ray scattering

Figures & data

Figure 1. Experimental setup showing the beam schematic and the modified quenching dilatometer with an entrance/exit window

Table 1. Mass fractions of alloying elements in the investigated aluminium wrought alloys

mass fraction in %		Si	Fe	Cu	Mn	Mg	Cr	Zn	Ti	Zr
EN AW-7150	EN 573-3	<0.12	<0.15	1.9–2.5	<0.1	2.0–2.7	<0.04	5.9–6.9	<0.06	0.08–0.15
	OES	0.02	0.05	2.04	0.04	2.15	<0.01	6.33	0.01	0.12
EN AW-6082	EN 573-3	0.7–1.3	<0.5	<0.1	0.4–1.0	0.6–1.2	<0.25	<0.2	<0.1	-
	OES	0.83	0.38	0.06	0.48	0.92	0.03	0.01	0.02	-

Figure 2. Schematic presentation of the time-temperature-profiles for the experiments

Figure 3. (a) diffraction pattern after cooling EN AW-7150 to room temperature at 0.3 K/s, as recorded by the imaging plate detector, (b) diffraction-data converted into a diffractogram at room temperature after cooling EN AW-7150 at 0.3 K/s

Table 2. Characteristic d-spacing, lattice parameters hkl and calculated 2-Theta angles specific to the applied wave-length ($\lambda$ = 0.012958 nm) with associated intensities for the structures of α-Al (fcc, a = 0.405 nm, η-MgZn₂ (hexagonal, a = 0.521 nm, c = 0.860 nm)and S-Al₂CuMg (orthorhombic, a = 0.400 nm, b = 0.923 nm, c = 0.714 nm)

d in Å	2-Theta in degree	hkl	Intensity in %	d in Å	2-Theta in degree	hkl	Intensity in %	d in Å	2-Theta in degree	hkl	Intensity in %
2.338	3.18	111	100	4.522	1.64	100	59	4.620	1.61	020	90
2.024	3.67	200	47	4.284	1.73	002	33	3.880	1.91	021	14
1.431	5.19	220	22	3.999	1.86	101	32	3.570	2.08	002	30
1.221	6.08	311	24	2.414	3.08	103	40	3.270	2.27	111	60
1.169	6.35	222	7	2.230	3.33	112	85	2.829	2.62	022	18
1.012	7.34	400	2	2.186	3.40	201	100	2.561	2.90	112	60
0.929	8.00	331	8	2.142	3.47	004	31	2.311	3.21	131	100
0.906	8.20	420	8	1.999	3.71	202	44	2.200	3.38	041	30
0.827	8.99	422	8	1.936	3.84	104	16	2.016	3.68	132	30
0.780	9.53	333	<1	1.773	4.19	203	21	1.999	3.71	113	90
…	…	…	…	…	…	…	…	…	…	…	…
α-Al				η-MgZn2				S-Al2CuMg

Table 3. Characteristic d-spacing, lattice parameters hkl and calculated 2-Theta angles specific to the applied wave-length ($\lambda$ = 0.012958 nm) with associated intensities for the structure of β-Mg₂Si (fcc, a = 0.639 nm)

d in Å	2-Theta in degree	hkl	Intensity in %
3.668	2.02	111	41
3.176	2.34	200	12
2.246	3.31	220	100
1.915	3.88	311	15
1.834	4.05	222	2
1.588	4.68	400	13
1.457	5.10	331	6
1.420	5.23	420	3
1.296	5.73	422	21
1.222	6.08	511	4
…	…	…	…
β-Mg2Si

Figure 4. Dynamic evolution of diffraction pattern during the cooling of EN AW-7150 at 0.3 K/s to room temperature after solution annealing at 480°C

Figure 5. Detailed view of the diffraction pattern during the cooling of EN AW-7150 at 0.3 K/s at different temperatures showing the shift of high-intensity peaks

Figure 6. Detailed view of specific diffraction peaks for η-MgZn₂ (1.73°), S-Al₂CuMg (2.27°) (EN AW-7150 in a) and β-Mg₂Si (2.02°) (EN AW-6082 in b) during cooling of a) EN AW-7150 at 0.3 K/s and b) EN°AW-6082 at 0.03 K/s. The background noise, which depends on 2-Theta angle and temperature can be seen

Figure 7. (a) detected diffraction counts for the 002 distance of the η-MgZn₂ structure formation in EN AW-7150 during cooling at 0.3 K/s for selected temperatures; (b) normalised signal step specific baselines used for peak area integration

Figure 8. Dynamic evolution of normalised WAXS peaks for EN AW-7150 during cooling at 0.3 K/s after solution treatment for (a) the η-MgZn₂ structure (002, 1.73°), (b) the S-Al₂CuMg phase structure (111, 2.27°) and (c) the β-Mg₂Si structure (111, 2.02°) during cooling of EN AW-6082 at 0.03 K/s

Figure 9. (a), (b), (c) integrated peak areas of η-MgZn₂, S-Al₂CuMg and β-Mg₂Si; (d), (e), (f) differentiation of the smoothed integral curve to the process variable ‘transformation rate’

Figure 10. DSC cooling curves of EN AW-7150 after solution treatment indicating a minimum of three precipitation reactions; DSC data adapted from [8]

Figure 11. Comparison of obtained WAXS results to DSC curves [8] during cooling of EN AW-7150 after solution treatment

Figure 12. DSC cooling curves for EN AW-6082 after solution treatment, indicating a minimum of two precipitation reactions; DSC data adapted from [10]

Figure 13. Comparison of WAXS results to DSC curves [10] during the cooling of EN AW-6082 after solution treatment

Figure 14. Improved continuous cooling precipitation diagram of EN AW-6082 after 560°C for 20 min, indicating the temperature ranges of overlapping precipitation reactions

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