Using high-speed scanning remelting technology to achieve AlSi10Mg laser powder bed fusion with excellent strength and plasticity properties

The development of additive manufacturing (AM) has profoundly changed the manufacturing industry, and this technology has been applied in fields such as food, medicine, automotive, and electronic components. Especially in the aerospace field, where extremely lightweight and high-strength (~500mpa) components are required, aluminum alloy additive manufacturing is considered a very promising solution. Shuoqing Shi and others from the State Key Laboratory of Solidification Processing of Northwestern Polytechnical University found that the limited mechanical properties of aluminum silicon alloys hindered their application under harsh and extreme conditions. The cracking tendency of high-strength aluminum alloys and the high cost of rare earth elements pose challenges to the large-scale application of aluminum alloys in additive manufacturing. The new practical high-speed scanning remelting technology proposed in this study enables Al Si alloys to have a significant proportion of microstructure and nano precipitates, with strength (496.1 ± 5.8 MPa) and plasticity (21.4 ± 0.9%) superior to the mechanical properties of aluminum alloys prepared by conventional methods. This in-situ microstructure control method has opened up new avenues for applications in harsh engineering environments.

Figure 1: Microstructure of LPBF and LPBF-HSR samples. Band contrast (BC), inverse polarization (IPF), and GND distribution of samples (a-a2) (i-i2). (b) (j) PF images of (a1) and (i1) respectively. (c-d) (k-l) Equivalent grain diameter and aspect ratio. SEM images and aspect ratios of (e-f) (m-n) cellular substructures. (g-h) (o-p) SEM images and size distribution of precipitated nanoparticles.

Figure 2: Temperature field and solidification conditions of the molten pool. (a-b) are the longitudinal sections of the melt pool temperature field for LPBF and LPBF-HSR specimens, respectively. Comparative analysis of isothermal melting interface temperature gradient G, growth rate R, and cooling rate T between LPBF and LPBF-HSR samples (c-d). (e) Solidification diagrams of G and R values under LPBF and HSSR conditions.

Figure 3 Uniaxial tensile performance. (a) Representative engineering stress-strain (σ - ε) curves. (b) The mechanical properties of current LPBF-HSR samples are compared with those of LPBF, heat treatment (HT), laser directed energy deposition (LDED), magnetic field (MF) applications, remelting, composite materials, and high-strength aluminum alloys. (c) The comparison chart of real stress (σ t) and work hardening rate (Zeta) with real strain (ε t) is shown in detail in the attached figure. (d) The work hardening index (n) values at different strain stages.

Figure 4 LUR tensile test and fracture analysis. (a) The LUR tensile test results of two samples. (b) The evolution of σ flow, σ back, and σ eff during tensile testing. (c) The proportion of σ eff to total σ at different strain levels (σ eff/σ flow). IPF and TF images near the (d-d ') (g-g') tensile fracture. GNDs and BC images of the blue boxed regions in (e-e '), (h-h'), (d), and (g). (f) (i) SEM images of the blue boxed areas in (e) and (h), respectively. (j-l) Evolution of dislocations near the fracture surface under different strains.

In summary, HSSR technology is considered a breakthrough and practical method for in-situ modification of the microstructure and mechanical properties of LPBF alloys, with great potential for application. Increasing the proportion of equiaxed refined grains can significantly alleviate strain localization at MPBs in the sample, thereby delaying debonding and improving the ductility of the sample. Refining the crystal cell structure, increasing grain boundary density, and precipitating nanoparticles can effectively improve work hardening ability and ultimately enhance tensile strength. The influence of HSSR treated Al Si alloy on anisotropy, fracture toughness, and fatigue performance is a highly concerned issue in the aerospace field and deserves further exploration.

The relevant research results were published in Materials Research Letters (Volume 12, 2024 Issue 9) under the title "Achieving superior strength ductility performance in laser powder bed fusion of AlSi10Mg via high-speed scanning refining". The first author of the paper is Shuoqing Shi, and the corresponding author is Yufan Zhao.

Source: Yangtze River Delta Laser Alliance