First Author: Qiao Qian

Corresponding authors: Dawei Guo, Yongyong Lin, Dawei Zhang, Lap Mou Tam 

Affiliated institutions: Institute for Development and Quality, Aerospace Engineering Equipment (Suzhou) Co., Ltd., University of Science and Technology Beijing, University of Macau

I. Technical Background and Challenges

• Pain points of traditional metal 3D printing: Current mainstream laser-based 3D printing technologies require melting metal during manufacturing, which can easily lead to defects such as porosity and thermal cracks, thereby compromising part quality.
• The Rise of Solid-State Additive Manufacturing: A technology called “Additive Friction Stir Deposition (AFSD)” has emerged. During processing, the metal does not melt but is instead “softened” through friction heat and pressure, allowing it to be layered and formed. This approach avoids the aforementioned drawbacks.
• Challenges Facing AFSD Technology: Traditional AFSD technology primarily relies on mechanical friction to generate heat. This heat is sometimes insufficient or unstable, resulting in poor material fluidity and inadequate bonding between layers. This compromises the overall strength and uniformity of the parts.

II. Innovative Solution: Hybrid Heat Source Technology

Researchers have proposed a novel method called Hybrid Heat Source Solid-State Additive Manufacturing (HHSAM).

Core Principle:

In addition to the mechanical friction heat generated by the traditional AFSD, an induction heating coil is introduced as an auxiliary heat source.

Working Method:

The coil is wrapped around the exterior of the machining tool, providing continuous and stable heat throughout the entire manufacturing process.  

Key Advantages:

• Precise Temperature Control: Enables more accurate regulation of processing temperatures.
• Enhanced Material Temperature: Significantly increases the temperature of metallic materials, improving their fluidity.
• Strengthened Bonding: Enhances the metallurgical bonding strength between layers.

III. Key Findings on Skill Enhancement

328.By comparing the new method (HHSAM) and the traditional method (AFSD), the study found that:

Significant improvement in temperature and fluidity

• The average temperature in the processing zone increased from 198°C to 318°C.
• Higher temperatures make the material more “soft,” enhancing its fluidity and facilitating thorough mixing and shaping.

Microstructure optimized

• Suppresses abnormal grain growth: Components produced using conventional AFSD often exhibit individual grains with excessive growth (AGG) after heat treatment, which degrades performance. HHSAM technology successfully avoids this issue, yielding a uniform and dense microstructure.
• Promotes beneficial phase formation: HHSAM technology facilitates the formation and enrichment of the strengthening phase Mg₂Si. These fine particles act like “pins,” preventing excessive grain growth during heat treatment and thereby enhancing material strength.

Comprehensive enhancement of mechanical properties

• Strength and toughness combined: After heat treatment, parts manufactured with HHSAM exhibit higher strength and superior toughness (elongation) in both horizontal and vertical directions.
• Balanced performance: Its comprehensive mechanical properties outperform multiple mainstream 3D printing technologies, achieving an excellent balance between high strength and high toughness.
• Fracture Mode Transformation: Fracture surfaces of HHSAM parts exhibit dense dimpling patterns characteristic of ductile fracture, indicating superior toughness.

Corrosion resistance is significantly improved.

HHSAM components exhibit superior corrosion resistance in saline environments. This advantage stems from their more uniform microstructure and increased presence of stable Mg₂Si strengthening phases, which mitigate electrochemical corrosion caused by compositional inhomogeneities.

IV. Research Findings and Future Prospects

• Key Findings: Hybrid Heat Source Solid-State Additive Manufacturing (HHSAM) represents an efficient and reliable novel approach to metal 3D printing. By incorporating auxiliary induction heating, it overcomes the thermal bottleneck inherent in conventional AFSD, successfully producing high-performance AA6061 aluminum alloy parts characterized by uniform structure, high strength, excellent toughness, and corrosion resistance.
• Application Prospects: This method offers a novel technical pathway for manufacturing large-scale, high-performance metal components—such as structural parts for aerospace and transportation sectors—with broad industrial application potential.

Image Analysis:

Fig. 1. Schematic diagram of solid-state manufacturing methods and the novel proposed hybrid heat-source solid-state manufacturing in this work.

Fig. 2. Photos and schematic diagrams of the (a) AFSD, (b) HHSAM processes and the applied (c) hollow tool. (d) Diagram of the inductive heating, (e) photos of the AFSDed and HHSAMed depositions based on the marked deposition path during the depositing process, and (f) the sampling diagram for properties analyses.

Fig. 3. In-situ monitoring data, including (a) temperature, (f) upsetting force (Fups), (g) spindle force (Fspi) and (h) spindle torque (Mspi), detected through the in-situ process monitoring kit for AFSD and HHSAM respectively. Temperature maps of AFSD (d) and HHSAM (e) obtained by FLIR, the temperature gradient along (b) Z and (c) X directions. (i) Schematic diagram of material deformation analysis.

Fig. 4. Metallographic pictures of the cross-sections of (a) AFSD, (b) HHSAM, (c) AFSD-HT and (d) HHSAM-HT.

Fig. 5. (1) Large-area and higher magnification (30 0 × and 10 0 0 ×) IPF images, (2) misorientation angle distribution and (3) PF images of (a) AFSD, (b) HHSAM, (c) AFSD-HT and (d) HHSAM-HT. The results of misorientation angle distribution and PF correspond to the large-area and 1000×magnifaction IPF images respectively.

Fig. 6. (a) Bright-field TEM images, (b) EDS mapping of the AA6061 specimen, (c) the corresponding SADP of the marked region in (a).

Fig. 7. (A) TEM images and corresponding EDS mapping. (B) High magnification HRTEM image focuses on the dislocations. (C) High magnification HRTEM images and IFFT patterns focus on the precipitations. Among that, (I), (II), (III) and (IV) represents AFSD, HHSAM, AFSD-HT and HHSAM-HT, respectively.

Fig. 8. Microhardness distribution of (a) AFSD, (b) HHSAM, (c) AFSD-HT and (d) HHSAM-HT along Z direction.

Fig. 9. Comparison stress-strain plots for the (a) as-fabricated and (b) heat-treated depositions along X and Z. (c) Tensile properties of the depositions. (d) Comparison of the results of elongation vs. UTS of the depositions in this study and those obtained by various AM methods.

Fig. 10. 3D images and high-magnification SEM images of fracture surfaces of various depositions: (a) AFSD, (b) HHSAM, (c) AFSD-HT and (d) HHSAM-HT; (e) 2D scanning profiles along the marked line in each image as given in (a)-(d).

Fig. 11. (a) Eocp vs. immersion time, (b) PD curves, (c) Nyquist and (d, e) Bode plots of various depositions.

Corresponding Author Profile

The Institute for Development and Quality, Macau (IDQ) is a Publicly Capitalized Non-profit Organization of the Macao Special Administrative Region. It has long served the field of public works quality control in the Macao SAR and conducts research in mechanical engineering areas such as metal forming technology and corrosion protection. IDQ is committed to application-oriented scientific research. IDQ has established a joint laboratory for solid phase processing technology with Aerospace Engineering Equipment (Suzhou) Co., Ltd. in the Guangdong-Macao In-Depth Cooperation Zone in Hengqin. IDQ has also established a joint laboratory for corrosion protection with the National Materials Corrosion and Protection Scientific Data Center at the Shunde Innovation School, University of Science and Technology Beijing.

Lap Mou Tam，PhD in Engineering, serves as Chairman of the Institute for Development and Quality, Macau, and Professor in the Department of Electrical and Mechanical Engineering at the University of Macau. He concurrently holds positions as Vice Chairman of the Chinese Society for Corrosion and Protection (CSCP) and Chief Scientist at Aerospace Engineering Equipment (Suzhou) Co., Ltd. His long-term research spans interdisciplinary fields including energy systems, thermal management, solid phase processing technology, corrosion-resistant material development, and wireless communication technology.

Cite this article

Qian Qiao, Chan Wa Tam, Wai I Lam, Kaiyuan Wang, Dawei Guo, Chi Tat Kwok, Yongyong Lin, Guoshun Yang, Hongchang Qian, Dawei Zhang, Xiaogang Li, Lap Mou Tam, Hybrid heat-source solid-state additive manufacturing: A method to fabricate high performance AA6061 deposition, J. Mater. Sci. Technol. 228 (2025) 107-124.