Kun Liu

Bio: Kun Liu is an academic researcher from Applied Science Private University. The author has contributed to research in topics: Alloy & Intermetallic. The author has an hindex of 16, co-authored 69 publications receiving 828 citations. Previous affiliations of Kun Liu include Université du Québec & Wenzhou University.

Deformation microstructures and strengthening mechanisms for the wire+arc additively manufactured Al-Mg4.5Mn alloy with inter-layer rolling

Abstract: Applying inter-layer rolling to the wire+arc additively manufacturing (WAAM) process with increasing loads of 15 kN, 30 kN and 45 kN, achieves excellent mechanical properties for 5087 (Al-Mg4.5-Mn) alloys. Compared with the as-deposited alloy, the average micro hardness, yield stress and ultimate tensile strength of 45 kN rolled alloys reached to 107.2 HV, 240 MPa and 344 MPa, which were enhanced by 40%, 69% and 18.2%, respectively. Primary coarse grain structures were found to become greatly refined with an evident rolling texture after deformation. The strengthening mechanisms mainly are deformation strengthening, grain refinement, and solution strengthening. Meanwhile, the elongation of rolled alloys stays over 20%. The plasticity was not obviously diminished compared with the as-deposited alloy. This is two times greater than the commercial wrought Al-Mg alloy with similar composition. The excellent plasticity may be chiefly due to grain refinement, pores closure and reduction, and grain recrystallization during the WAAM re-heating process. The combination process of rolling deformation with WAAM deposition is an effective technique in refining microstructure and improving mechanical properties for AM aluminum alloys.

Solidification of Iron-Rich Intermetallic Phases in Al-4.5Cu-0.3Fe Cast Alloy

Abstract: The iron-rich intermetallics in A206 type cast aluminum alloy (Al-4.5Cu-0.3Fe) were investigated using thermal analysis, interrupted quenching testing, and differential scanning calorimetry (DSC). An optical microscope with image analysis and scanning electron microscopy were used to identify and quantify the iron-rich intermetallics. Basically, two kinds of iron-rich intermetallics, Chinese script Al15(FeMn)3(SiCu)2 (α-Fe) and platelet Al7Cu2(FeMn) or Al7Cu2Fe (β-Fe), are found in the final microstructures of the A206 cast alloys. All the possible solidification reactions, precipitation temperatures, and nucleation mechanisms for the iron-rich phases were investigated systematically. It is found that both α-Fe and β-Fe phases can precipitate on the oxide films. The α-Fe can also nucleate on Al6(FeMnCu) and Al3Ti particles. In addition, the previously formed α-Fe phase is also favorable for the nucleation of the β-Fe phase formed subsequently. These nucleation events were not only observed metallographically but also supported by the calculated planar disregistries. A possible nucleation hierarchy has been suggested.

Current Status and Perspectives on Wire and Arc Additive Manufacturing (WAAM)

Abstract: Additive manufacturing has revolutionized the manufacturing paradigm in recent years due to the possibility of creating complex shaped three-dimensional parts which can be difficult or impossible to obtain by conventional manufacturing processes. Among the different additive manufacturing techniques, wire and arc additive manufacturing (WAAM) is suitable to produce large metallic parts owing to the high deposition rates achieved, which are significantly larger than powder-bed techniques, for example. The interest in WAAM is steadily increasing, and consequently, significant research efforts are underway. This review paper aims to provide an overview of the most significant achievements in WAAM, highlighting process developments and variants to control the microstructure, mechanical properties, and defect generation in the as-built parts; the most relevant engineering materials used; the main deposition strategies adopted to minimize residual stresses and the effect of post-processing heat treatments to improve the mechanical properties of the parts. An important aspect that still hinders this technology is certification and nondestructive testing of the parts, and this is discussed. Finally, a general perspective of future advancements is presented.

A review of wire arc additive manufacturing and advances in wire arc additive manufacturing of aluminium

Abstract: Although wire arc additive manufacturing (WAAM) has proven its capability of fulfilling demands of production of medium-to-large-scale components for automotive and allied sectors made up of alumin...

Surface post-treatments for metal additive manufacturing: Progress, challenges, and opportunities

Abstract: Metal additive manufacturing is a rapidly expanding area owing to its capacity to fabricate parts of intricate geometries with customized features for a wide range of applications. However, these parts generally exhibit inadequate and poor surface quality in the as-built configuration. The surface imperfections and defects ranging from staircase effect due to the layer by layer nature of the deposition techniques, partially fused feedstock material, balling effects, spatters, or inadequate fusion lead to a notably irregular surface morphology. This high surface roughness can significantly deteriorate the performance of the additive manufactured parts imposing a substantial limit on their prospective applications; for instance, fatigue performance, wear and scratch resistance, dimensional accuracy, and aesthetical aspects can be highly affected by these surface defects. A great effort has been lately dedicated to developing post-treatments for improving the surface quality of additively manufactured metallic parts. In this paper, various treatments applied to as-built samples fabricated using different additive manufacturing technologies are introduced and discussed. The advances in this area are highlighted, and the results obtained from different categories of post-treatments are compared and reviewed. Challenges and opportunities to gain more control on the surface roughness of additively manufactured metallic parts through the application of these post-treatments are addressed.

Laser powder bed fusion for metal additive manufacturing: perspectives on recent developments

Abstract: While significant progress has been made in laser powder bed fusion (L-PBF) for metal additive manufacturing (AM), there is still limited large scale adoption of this advanced manufacturing techniq