Elimination of extraordinarily high cracking susceptibility of aluminum alloy fabricated by laser powder bed fusion

doi:10.1016/j.jmst.2021.06.023

Abstract

Abstract:

Using the calculation of phase diagrams approach and Scheil solidification modeling, the Al-2.5Mg-1.0Ni-0.4Sc-0.1Zr alloy was designed, intentionally with an extraordinarily high cracking susceptibility, making it prime for solidification cracking during laser powder bed fusion. This study demonstrates the ability to mitigate even the most extreme solidification cracking tendencies in aluminum alloys with only minor alloying additions of Sc and Zr, 0.5 wt.% max. Furthermore, by employing a simple direct ageing heat treatment, good tensile mechanical properties were observed with a yield strength of 308 MPa, an ultimate tensile strength of 390 MPa, and a total elongation of 11%.

Key words: Additive manufacturing, Cracking susceptibility, Aluminum alloy, CALPHAD, Mechanical properties

Holden Hyer, Le Zhou, Sharon Park, Thinh Huynh, Abhishek Mehta, Saket Thapliyal, Rajiv S. Mishra, Yongho Sohn. Elimination of extraordinarily high cracking susceptibility of aluminum alloy fabricated by laser powder bed fusion[J]. J. Mater. Sci. Technol., 2022, 103: 50-58.

Figures/Tables 6

Fig. 1. Temperature vs. fS1/2 curves for (a) common commercial Al-alloys and for (b) Al-Mg alloys examined in this study. (c) The maximum crack susceptibility index, |dT/dfS1/2|, for different Al-alloys shows that Al-2.5Mg-1.0Ni base alloy has an extremely high susceptibility index.

Fig. 2. (a) Relative density of cube samples measured by Archimedes method and (b) Vickers hardness for the cubes processed at varying laser power and scan speed. A dashed line was added to each of the curves to suggest the overall trend of the data.

Fig. 3. Optical images of the cross-section parallel to the build direction of the AlMgNiScZr cubes processed at varying laser power and scan speed.

Fig. 4. Optical micrographs of LPBF AlMgNiScZr cross-sections (a) along the build direction and (b) perpendicular to the build direction. Backscatter electron micrographs of an individual melt pool at (c) low and (d) high magnification. EBSD grain mapping at (e) low and (f) high magnification.

Fig. 5. (a) Age hardening curve of AlMgNiScZr Heat Treated at 290 °C and (b) subsequent tensile stress-stress curves both after LPBF processing and after peak age hardening. A dashed line was added to the curve in (a) to suggest the overall trend of the data.

Table 1 Tensile mechanical properties of the AlMgNiScZr alloy compared with already existing alloys from the literature.

Alloy Description	Yield Strength (MPa)	Ultimate Tensile Strength (MPa)	Percent Strain	Refs.
AlMgNiScZr As-built	149.2 ± 0.37	266.9 ± 1.98	17.3 ± 0.9	This Study
AlMgNiScZr Heat Treated	308.0 ± 12.46	390.3 ± 9.15	11.2 ± 0.7	This Study
AlZnMgScZr As-Built	283.5	386.0	18.4	[6]
AlZnMgScZr Heat Treated	418.3	435.7	11.1	[6]
Al-3.66Mg-1.57Zr As-Built	349	383	19.5	[29]
Al-3.66Mg-1.57Zr Heat Treated	365	389	23.9	[29]
AA5083+0.7Zr As-Built	212.2	316.7	22.3	[4]
AA5083+0.7Zr Heat Treated	318.7	391.1	14.1	[4]
AA6061+1Zr As-Built	210.3	268.1	26.5	[7]
AA6061+1Zr Heat Treated	299.8	327.3	13.9	[7]
AA7075+Zr Heat Treated	325-373	383-417	3.8-5.4	[14]
AA7075 T6 Heat Treated	505	570	11	[30]
AA5083 H343	285	345	9	[30]
AA6061 T6 Heat Treated	275	310	17	[30]

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