The second-generation aluminum-magnesium-scandium (Al-Mg-Sc) alloy, which is often referred to as Scalmalloy®, has been developed as a high-strength aluminum alloy for selective laser melting (SLM). The high-cooling rates of melt pools during SLM establishes the thermodynamic conditions for a fine-grained crack-free aluminum structure saturated with fine precipitates of the ceramic phase Al₃-Sc. The precipitation allows tensile and fatigue strength of Scalmalloy® to exceed those of AlSi10Mg by ~70%. Knowledge about properties of other additive manufacturing processes with slower cooling rates is currently not available. In this study, two batches of Scalmalloy® processed by SLM and laser metal deposition (LMD) are compared regarding microstructure-induced properties. Microstructural strengthening mechanisms behind enhanced strength and ductility are investigated by scanning electron microscopy (SEM). Fatigue damage mechanisms in low-cycle (LCF) to high-cycle fatigue (HCF) are a subject of study in a combined strategy of experimental and statistical modeling for calculation of Woehler curves in the respective regimes. Modeling efforts are supported by non-destructive defect characterization in an X-ray computed tomography (µ-CT) platform. The investigations show that Scalmalloy® specimens produced by LMD are prone to extensive porosity, contrary to SLM specimens, which is translated to ~30% lower fatigue strength.

Comparison of Microstructure and Mechanical Properties of Scalmalloy® Produced by Selective Laser Melting and Laser Metal Deposition.

https://hal.archives-ouvertes.fr/hal-03059610/document

Reducing hot tearing by grain boundary segregation engineering in additive manufacturing: example of an AlxCoCrFeNi high-entropy alloy

7XXX series aluminum alloys (Al 7XXX alloys) are widely used in bearing components, such as aircraft frame, spars and stringers, for their high specific strength, high specific stiffness, high toughness, excellent processing, and welding performance. Therefore, Al 7XXX alloys are the most important structural materials in aviation. In this present review, the development tendency and the main applications of Al 7XXX alloys for aircraft structures are introduced, and the existing problems are simply discussed. Also, the heat treatment processes for improving the properties are compared and analyzed. It is the most important measures that optimizing alloy composition and improving heat treatment process are to enhance the comprehensive properties of Al 7XXX alloys. Among the method, solid solution, quenching, and aging of Al 7XXX alloys are the most significant. We introduce the effects of the three methods on the properties, and forecast the development direction of the properties, compositions, and heat treatments and the solution to the corrosion prediction problem for the next generation of Al 7XXX alloys for aircraft structures. The next generation of Al 7XXX alloys should be higher strength, higher toughness, higher damage tolerance, higher hardenability, and better corrosion resistance. It is urgent requirements to develop or invent new heat treatment regime. We should construct a novel corrosion prediction model for Al 7XXX alloys via confirming the surface corrosion environments and selecting the accurate and reliable electrochemical measurements.

The Advancement of 7XXX Series Aluminum Alloys for Aircraft Structures: A Review

Ti/TiBCN coatings were fabricated on the 7075 aluminum alloy by laser cladding. The influence of TiBCN content on microstructure, micro-hardness, electrochemical corrosion and wear resistance of the cladding coatings were studied by SEM, XRD, Vickers micro-hardness tester, a typical three-electrode electrochemical workstation and straight-line-reciprocating dry sliding wear tester, respectively. The results showed that, when TiBCN content was 15 wt%, the microstructure of coating zone mainly composed of equiaxed grains and white lath-like crystals and that of transition zone mainly consisted of the elongated dendrite crystals and white small particles. Furthermore, the average hardness of the Ti/TiBCN cladding coating is 750HV0.2, which was about 5 times higher than that of the substrate (~ 127HV0.2), and the corrosion potential (Ecorr) reached − 1.271 V and the corrosion current density (Icorr) was 3.155e− 005 A/cm2, which was one magnitude low than that of the substrate (2.269e− 004 A/cm2). The narrow and shallow plowing grooves uniformly distributed on the worn surface and have less wear damage and the mass loss of the cladding coating was only 2.4 mg in 20 min.

Microstructure and properties of Ti/TiBCN coating on 7075 aluminum alloy by laser cladding

The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, the high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.

Selective Laser Melting of Aluminum and Its Alloys.

Laser metal deposition of nickel coated Al 7050 alloy

Direct Laser Metal Deposition of Al 7050 Alloy

Various additive manufacturing techniques have been able to manufacture Al-Si hypo- and hyper-eutectic alloys but practical implementation of additive manufacturing of Al-Si alloys in automotive industry still remains a big challenge. This paper deals with the challenges of building tall wall and cuboid shapes eutectic Al-Si components by direct laser metal deposition technique for automotive applications. Microstructural investigation using optical and scanning electron microscopy revealed a 99.9% dense component with very fine hypoeutectic microstructure. Tensile test showed an impressive elongation of 9% with an ultimate tensile strength of 225 MPa. This investigation revealed that direct laser metal deposition could be successfully implemented on automotive shock tower hood without any distortion or bending. This paper also presents the effect of various laser deposition parameters like laser power, powder flow rate, and scanning speed on the microstructure and mechanical properties distribution from substrate to deposit.

Direct Laser Metal Deposition of Eutectic Al-Si Alloy for Automotive Applications

/pdf/fabrication-of-al-11-2si-components-by-direct-laser-metal-1o70qjjqw4.pdf

Fabrication of Al-11.2Si Components by Direct Laser Metal Deposition for Automotive Applications

Laser metal-deposited Al 7050 alloy exhibits reduced Mg and Zn content compared to parent composition due to substantial evaporation. This paper presents a technique to investigate various Al 7xxx alloy compositions in a single coupon. In this investigation, a gradient sample of Al 7050/Al50Mg50 was fabricated layer-by-layer by the gradual addition of Al50Mg50 alloy with the Al 7050 powder. A correlation was developed between Mg content in powder feed and the resulting gradient deposit. Microscopy investigation revealed that there were no major defects in gradient sample such as porosity or lack of fusion. Formation of strengthening precipitates primarily Al3Mg2 and MgZn2 was escalated with the gradual addition of Mg from bottom to the top layer of the Al 7050/Al50Mg50 gradient material. The EDS investigation showed that with the addition of more Mg, respective loss increases in the subsequent layer as compared to a loss of Mg in the previous layer. Microhardness gradually increased from 94 to 154 HV corresponding to Mg content of 2.8 to 23 wt pct in the first and last layer, respectively. This technique is very useful to develop new alloys by studying various compositions in one sample saving time and effort.

Amrinder Singh

Papers

Laser metal deposition of nickel coated Al 7050 alloy

Direct Laser Metal Deposition of Al 7050 Alloy

Direct Laser Metal Deposition of Eutectic Al-Si Alloy for Automotive Applications

Fabrication of Al-11.2Si Components by Direct Laser Metal Deposition for Automotive Applications

Laser Metal Deposition of Al-7050/Al50Mg50 Gradient Material