Aluminium alloy

An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils and extrusions. Cast aluminium alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminium alloy system is Al–Si, where the high levels of silicon (4–13%) contribute to give good casting characteristics. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed mostly of aluminium have been very important i

Additive Manufacturing of L12 Precipitate Strengthened Nickel and Aluminum Alloys

Seth James Griffiths

Metal Additive Manufacturing (AM) technologies have enabled the manufacturing of parts with complex geometries that were previously not feasible with conventional manufacturing. Unfortunately, many commercial engineering alloys (with the exception of alloys for welding) were designed with conventional manufacturing in mind and can behave poorly in the rapid solidification and thermal conditions that go along with AM. Research is needed to optimize the higher performance engineering alloys, such as pre-cipitation hardened alloys, for AM. One important class of precipitates in both the nick-el-base and aluminum-base superalloys is the intermetallic L12 âstructured (Strukturbericht notation) intermetallics. Many scientific challenges must be overcome prior to widespread industrial usage of these alloys. AM of L12-strengthened Ni-base superalloys results in extensive micro-cracking and AM of L12-strengthened Al-base alloys has been successful but requires further research to understand the material be-havior. This thesis focuses on overcoming the scientific challenges for the AM of L12-strengthened alloys. A new Al-Mg-Zr alloy strengthened via L12-structured Al3Zr precipitates, AddalloyÂ®,was successfully fabricated for the first time with Laser-Powder Bed Fusion (L-PPF). The as-fabricated Al-Mg-Zr alloy displayed a unique bimodal grain structure: (i) the bottom of the melt pools consisted of fine equiaxed grains (~1 Âµm) and (ii) the top of the melt pool consisted of columnar grains (up to 40 Âµm long). The bimodal microstructure was at-tributed to the changing solidification conditions during the lifetime of the melt. A new microstructure modification strategy, laser rescanning, was shown to refine the micro-structure. The grain refinement was attributed to the reduced melt pool depths of the additional scans, thus breaking up the previously solidified columnar grains. Scanning transmission electron microscopy (STEM) investigations of peak-aged (400ËC, 8 h) samples reveal both continuous (~2 nm in diameter) and discontinuous (~5 nm wide and hundreds of nanometers long) coherent, secondary L12-Al3Zr precipitates. The Al-Mg-Zr in the peak aged (400ËC, 8 h) condition had a 385 MPa yield strength and a 19% elongation at fracture. The excellent combination of strength and ductility was attribut-ed to the bimodal microstructure. For short-term elevated temperature yield tests, as-fabricated samples displayed higher yield strengths than peak-aged samples at temper-atures above 150ËC (e.g., 87 vs 24 MPa at 260ËC). For longer term creep tests at 260 ËC, both as-fabricated and peak-aged samples displayed near-identical creep behavior. The reduced elevated temperature performance of the peak aged samples was attributed to coarsening of grain-boundary precipitates during aging, decreasing their ability to in-hibit grain-boundary sliding (GBS) of the fine equiaxed grains. The micro-cracking of CM24LC, a Ni-base superalloy, was attributed to both solidifica-tion and liquation cracking. Based on experimental evidence, reduction in the solidifica-tion interval of CM247LC was investigated as a candidate for micro-crack mitigation and a new alloy was developed. As Hf is found to have a significant influence on the freezing range of the alloy, a new CM247LC without Hf was produced and tested. Sam-ples fabricated with the Hf-free CM247LC, CM247LC NHf, in combination with opti-mized processing conditions exhibit a reduction in crack density of 98%.

EPFL2020

Development of High-Strength Aluminum Alloys for Additive Manufacturing

Marvin Lennard Schuster

Metal additive manufacturing (AM) offers the possibility to rapidly produce complex geometries that are not achievable with conventional manufacturing methods. The two most common technologies, Laser Powder Bed Fusion (LPBF) and Direct Metal Deposition (DMD), are characterized by high process temperatures, fast heating, and cooling rates, and an associated far-from-equilibrium solidification. This is problematic when processing materials that were developed and optimized many years ago for conventional manufacturing processes. Common difficulties are the occurrence of gas pores in the component, which are caused by the evaporation of volatile alloying elements during the process, the formation of hot cracks due to large solidification intervals, and the formation of metastable phases. For the processing of high-strength, precipitation-hardening Al-Cu aluminum alloys, this prevents the use of non-modified conventional alloys. However, the development of novel alloys tailored to these processes not only allows these difficulties to be overcome but also opens up the possibility of improving material properties through the targeted exploitation of process-inherent properties. This includes the processing of oxide particle-reinforced alloys, which can not be produced by conventional casting processes. The standard heat treatment usually performed for precipitation hardening, which has also been optimized for conventional materials, must be adapted accordingly to achieve optimum material properties. Within the scope of this work, the microstructure, precipitation, and defect formation after LPBF as well as the heat treatment behavior are thoroughly investigated based on an Al-Cu-Mg-Zr alloy for the first time. The obtained findings are applied to design a novel 2618 Al-Cu alloy for LPBF and DMD, with suitable heat treatment being developed for LPBF. The alloy is characterized with respect to microstructure, precipitation formation, and mechanical properties before, during, and after heat treatment. Furthermore, by modifying elemental Al-Zr powder blends with nm-sized Al2O3, an oxide dispersion strengthened alloy is produced by LPBF and investigated in detail.

EPFL2022

Additive Manufacturing of L12 Precipitate Strengthened Nickel and Aluminum Alloys

Seth James Griffiths

EPFL2020

Development of High-Strength Aluminum Alloys for Additive Manufacturing

Marvin Lennard Schuster

EPFL2022

Additive Manufacturing of L12 Precipitate Strengthened Nickel and Aluminum Alloys

Development of High-Strength Aluminum Alloys for Additive Manufacturing

Modelling of microporosity, macroporosity and pipe shrinkage formation during the solidification of aluminium alloys, using a mushy zone refinement method

Additive Manufacturing of L12 Precipitate Strengthened Nickel and Aluminum Alloys

Development of High-Strength Aluminum Alloys for Additive Manufacturing

Modelling of microporosity, macroporosity and pipe shrinkage formation during the solidification of aluminium alloys, using a mushy zone refinement method