Comparison of Rare Earth Refinement in 4130 and HY100

Solidification based grain refinement has gained wide interest by both researchers and industry. This method provides a route for refinement in processes where thermomechanical approaches are ineffective. Prior research into 4130 and HY100 found very different responses when rare earth additions were made. The 4130 was effectively refined while HY100 showed no response. The cause of this difference was not determined. The research presented in this paper examined heats of 4130 and HY100 with rare earth silicide or EGR additions. Characterization included macrostructure examination, mechanical testing, thermal analysis, and electron microscopy. Refinement was observed only in the treated 4130 heats and corresponded to an increase in the peritectic temperature. The HY100 heats had no changes in macrostructure or solidification reactions. Rare earth containing inclusions of similar compositions were observed in the treated 4130 and HY100 heats. These inclusions appear to be a good fit for austenite based on the 4130 data. It was proposed that the unresponsiveness of HY100 was due to the strong segregation of nickel before the peritectic in that alloy. Nickel promotes austenite, and its segregation may provide a stronger driving force for its formation than the energy barrier reduction caused by the presence of rare earth inclusions.

Role of Gd addition on machinability of Al-15%Mg2Si in-situ composite during dry turning

Recently, Al-Mg2Si in-situ composites have achieved considerable attention due to their excellent physical and mechanical properties. In fact, there are some limitations of knowledge regarding the machinability characteristics of these composites - particularly when being inoculated with rare earth additions. This study in turn aimed to investigate the influence of machining parameters as well as Gd addition on the machinability of Al-15%Mg2Si composite. To examine the effect of modifier (1.0 wt. % Gd) and machining parameters (feed rate, cutting speed), microstructural evolution, surface roughness (Ra) and cutting force (Fc) were evaluated during dry turning. The results revealed that Gd addition as modifier element led to better surface roughness and higher cutting force owning to the modification of Mg2Si particle structure as well as the formation of Gd intermetallic compounds.

Influence of Rare Earth Additions to an Inconel 718 Alloy

This work analyzes the effect of rare earth additions to an Inconel 718 superalloy; for this purpose, two 8 kg ingots of a commercial composition of Inconel 718 were made in a vacuum induction furnace. One of them (In718) with the base composition and the other one (In718RE) with an addition of 0.04wt% of mischmetal (rare earths alloy based on cerium and lanthanum). Both alloys were cast into metallic molds into the vacuum chamber and let to solidify. The alloys were then solubilized for two hours at 1155 °C to eliminate deleterious phases, rolled at 1100 °C to get a reduction of 50% in thickness, then aged for 16 hours at 720 °C and 620 °C by 8 hours each. A complete microstructural characterization was undertaken by optical and electronic (SEM and TEM) microscopy and X-ray diffraction. Mechanical characterization was done by hardness tests, tensile and Charpy impact tests. Results show a slight improvement of the tensile and hardness values for the alloy with rare earth additions. However, no notorious difference was observed during the impact tests, since both alloys show the same values. These mechanical results are discussed in terms of the obtained microstructure. Both alloys are mainly composed by γ, γ´, γ´´ and carbides. It was observed that primary carbides nucleate rare earth particles; therefore, higher number of carbides and of larger size (according to a size distribution) are observed in the alloy with rare earth additions. The presence of such carbides prevents the grain growth during the thermomechanical processing which in turn improve the mechanical properties.

Influence of Rare Earth Additions on the Microstructure and Mechanical Properties of Al7Si0.3Mg Alloys Processed by Semi-Solid Die Casting and Gravity Die Casting

Microstructures with fine globular grains and refined eutectic structures are important to enhance the mechanical properties of A356 alloys processed by semi-solid and gravity die casting. Rare earth (RE) additions have been shown to be capable of refining both the α-Al particles as well as modify the eutectic phase of alloys. In semi-solid die casting, Al7Si0.3Mg alloys with RE concentrations (0, 0.1 and 0.4 wt.%) were used to prepare semi-solid slurries using the SEED (Swirling Enthalpy Equilibrium Device) method, and subsequently semi-solid die cast. The same compositions of alloys were also applied to gravity die casting. The microstructure and mechanical properties of castings in two processes have been characterized. Compared to the grains produced in gravity die casting, globular grains with small size (260 μm) in the semi-solid die casting significantly enhance the UTS and elongation of alloys. Although the size of grains had no change with increasing RE concentrations in alloys. The Al-Si eutectics were changed to refined morphology with the 0.1 wt.% RE addition, which enhanced the ductility of alloys in two processes. When increasing the RE addition to 0.4 wt.%, the RE-rich phases precipitated at grain boundaries, which decreased the UTS and elongation of alloys.