Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

doi:10.1007/s40195-017-0586-3

Abstract

Abstract:

The effect of peak temperature (T _p) at 200, 300, 400, 500 and 550 °C on the microstructural evolution and softening behavior of the simulated heat-affected zone (HAZ) was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200-500 °C was comparable, but the number density of the strengthening precipitates (GP zones/θ′) decreased with increasing T _p. At a T _p of 550 °C, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at T _p values in the range of 200-400 °C. Increasing the T _p to 500 °C and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.

Key words: 2219 aluminum alloy, Peak temperature of thermal cycles, Electron-backscatter diffraction (EBSD), Softening behavior, Precipitates

Xin-Jie Di, Hui-Juan Xie, Cui-Xin Chen, Cai-Yan Deng, Dong-Po Wang. Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(12): 1177-1184.

Figures/Tables 12

Table 1 Mechanical properties of the 2219-T87 aluminum alloy

Yield strength (Re/MPa)	Ultimate tensile strength (Rm/MPa)	Elongation (δ/%)	Hardness (HV_0.98N)
395	475	10	135

Fig. 1 Thermal cycles simulated the fusion welding process

Fig. 2 Dimensions of the micro-tensile specimens (in mm)

Fig. 3 Orientation maps of the HAZ samples with different T p: a 200 °C, b 300 °C, c 400 °C, d 500 °C, e 550 °C

Fig. 4 EBSD determined histograms of the boundary misorientation distribution in the HAZ samples with different T p

Fig. 5 Distribution of the grain diameter at T p of 200, 400 and 550 °C

Table 2 Taylor factor (M) at different T p

T _p	200 °C	300 °C	400 °C	500 °C	550 °C
Taylor factor (M)	2.84	2.84	2.84	2.93	3.12

Fig. 6 TEM micrographs of the simulated HAZ at different T p and the selected area electron diffraction patterns from this region: a 200 °C, b 300 °C, c 400 °C, d 500 °C, e 550 °C

Table 3 Quantitative analysis results of the microstructures of the simulated HAZ at different T p

T _p	200 °C	300 °C	400 °C	500 °C	550 °C
Length of the θ′ phase (nm)	55.6	62.5	85.5	-	-
Thickness of the θ′ phase (nm)	7.0	7.3	13.2	-	-
f _v of the θ′ phase (%)	17.7	16.5	11.6	-	-
f _v of the θ′ (form from θ′) (%)	-	-	4.4	9.6	9.5
Lattice parameter of α (nm)	0.40409	0.40425	0.40439	0.40421	0.40413
Cu concentration in α (wt%)	4.22	3.45	2.77	3.64	4.03

Fig. 7 XRD patterns of the simulated HAZ: a XRD pattern for 2θ from 35° to 110°, b the magnified image of the first two peaks

Fig. 8 Micro-hardness profile and tensile strength profile for the base metal (20 °C) and the thermally cycled specimens at different T p

Fig. 9 SEM micrograph and the EDS analysis of the lamellar particle at T p of 550 °C

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