Influence of calcium on the microstructure and properties of an Al-7Si-0.3Mg-xFe alloy

The effect of Ca addition on the microstructure, physical characteristics (density/porosity), and mechanical properties (tensile and impact strength) has been investigated in an Al-7Si-0.3Mg-xFe (x=0.2, 0.4, and 0.7) alloy. The size of Al-Fe intermetallic platelets (β-Al₅FeSi) increased with increasing Fe content. The addition of Ca modified the eutectic microstructure and also reduced the size of intermetallic Fe-platelets, causing improved elongation and impact strengths. A low level of Ca addition (39 ppm) reduced the proosity of the alloys. The tensile strength was decreased marginally with Ca addition. However, Ca addition improved the ductility of the alloy by 18.3, 16.7, and 44 pct and the impact strength by 44, 48, and 15.8 pct for Fe contents of 0.2, 0.4, and 0.7 pct, respectively.     

A study of the influence of mischmetal additions to ai-7si-0.3mg (lm 25/356) alloy

This article deals with the effect of 0.25-1.5 wt pct mischmetal (MM) addition on the mechanical properties, microstructure, electrical conductivity, and fracture behavior of cast Al-7Si-0.3Mg (LM 25/356) alloy. Modification of eutectic silicon by MM is compared with strontium modification in terms of microstructure, mechanical properties, and fading behavior. Loss of magnesium encountered on holding the molten alloy and its resultant effect on mechanical properties of alloys modified with MM and Sr are compared with those in the unmodified alloy.     

Evolution of Intermetallics,Dispersoids, and Elevated Temperature Properties at Various Fe Contents in Al-Mn-Mg 3004 Alloys

Nowadays, great interests are rising on aluminum alloys for the applications at elevated temperature, driven by the automotive and aerospace industries requiring high strength, light weight, and low-cost engineering materials. As one of the most promising candidates, Al-Mn-Mg 3004 alloys have been found to possess considerably high mechanical properties and creep resistance at elevated temperature resulted from the precipitation of a large number of thermally stable dispersoids during heat treatment. In present work, the effect of Fe contents on the evolution of microstructure as well as high-temperature properties of 3004 alloys has been investigated. Results show that the dominant intermetallic changes from α-Al(MnFe)Si at 0.1 wt pct Fe to Al₆(MnFe) at both 0.3 and 0.6 wt pct Fe. In the Fe range of 0.1–0.6 wt pct studied, a significant improvement on mechanical properties at elevated temperature has been observed due to the precipitation of dispersoids, and the best combination of yield strength and creep resistance at 573 K (300 °C) is obtained in the 0.3 wt pct Fe alloy with the finest size and highest volume fraction of dispersoids. The superior properties obtained at 573 K (300 °C) make 3004 alloys more promising for high-temperature applications. The relationship between the Fe content and the dispersoid precipitation as well as the materials properties has been discussed.     

Creep and microstructure of magnesium-aluminum-calcium based alloys

This article describes the creep and microstructure of Mg-Al-Ca-based magnesium alloys (designated as ACX alloys, where A stands for aluminum; C for calcium; and X for strontium or silicon) developed for automotive powertrain applications. Important creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Creep properties of the new alloys are significantly better than those of the AE42 (Mg-4 pct* Al-2 pct RE**) alloy, which is the benchmark creep-resistant magnesium die-casting alloy. Creep mechanisms for different temperature/stress regimes are proposed. A ternary intermetallic phase, (Mg,Al)₂Ca, was identified in the microstructure of the ACX alloys and is proposed to be responsible for the improved creep resistance of the alloys. All concentrations in wt. pct, unless otherwise stated. RE stands for a combination of rare earth elements, i.e., misch metal, in this case.     

Effect of Sn on microstructure and mechanical properties of Ti-base dendrite/ultrafine-structured multicomponent alloys

Ti_57−x Cu₁₅Ni₁₄Sn_4+x Nb₁₀ (x = 0, 5, or 10) alloys were prepared by copper mold casting. At Sn = 4 at. pct, a dendrite/ultrafine-structured multicomponent alloy was obtained, which exhibits 1271 MPa yield strength, 77 GPa Young’s modulus, and 2 pct plasticity at room temperature for 3-mm-diameter samples. The cooling rate significantly affects the as-cast microstructure and the mechanical properties. For 5-mm-diameter samples, the alloy exhibits 1226 MPa yield strength, 63 GPa Young’s modulus, and 2.5 pct plasticity. At Sn = 9 at. pct, Ti-, Sn-, and Nb-rich particles precipitate primarily. This near-hypereutectic alloy composition leads to the precipitation of intermetallics, which deteriorate the mechanical properties and result in the coexistence of ductile and brittle fracture mechanisms. At Sn = 14 at. pct, the alloy composition is completely in the intermetallic region, thus inducing the formation of Ti₂Cu, Ti₂Ni, and Ti₃Sn intermetallics. The alloy becomes very brittle because the intermetallic compounds dominate the fracture process.     

Effects of Be and Fe additions on the microstructure and mechanical properties of A357.0 alloys

A357 hypoeutectic alloy is a heat-treatable Al-Si-Mg system with a nominal composition of Al-7 pct Si and about 0.6 pct Mg have widespreaded applications, especially in the aerospace and automotive industries. The purpose of this study was to determine the influences of Be and Fe content on the microstructure and mechanical properties of A357.0 alloys. Distinct morphologies were discerned between Be-containing and Be-free alloys. The Be-free alloys contain larger amount of iron-bearing phases with Mg than in Be-containing alloys. The addition of Be can change the plateletlike structure of iron-bearing phases to a comparatively harmless round nodular form. Also, the amounts of iron-rich phases are significantly lower and the silicon particles are smaller and more spherical in the Be-containing alloys. Small amounts of Be in A357.0 caused significant increases in the precipitation kinetics of Mg₂Si. It was found that the addition of Be lowers the ternary and binary eutectic melting point. The amount of Mg available to form the major strengthening phase Mg₂Si is increased promoting the tensile strength of A357.0 casting. The tensile properties were improved with decreasing Fe content and the addition of Be. The effect is more apparent in the higher Fe alloys than that in the lower Fe alloys.     

Microstructure and Mechanical Properties of Extruded Magnesium-Aluminum-Cerium Alloy Tubes

Current commercial magnesium extrusion alloys do not offer desirable combinations of strength, ductility, and extrusion speed for automotive structural applications. The effect of small additions of cerium (Ce) to pure magnesium (Mg) and Mg-3 pct Al alloy extruded tubes has been studied. The results suggest that 0.2 pct Ce addition can significantly improve the extrudability and mechanical properties of the Mg extrusions. The improvement in mechanical properties is due to grain refinement and dispersion strengthening provided by the Mg₁₂Ce particles and the beneficial texture obtained. Higher Ce contents further increase strength, but significantly reduce ductility and cause excessive surface oxidation during extrusion. The beneficial effect of 0.2 pct Ce on mechanical properties of pure Mg is not observed when it is added to Mg-3 pct Al alloy, due to the higher affinity of Ce to Al to form the Al₁₁Ce₃ phase in the Mg-Al-Ce ternary alloys. The Mg-0.2 pct Ce alloy is a promising base alloy for further development in automotive applications; however, Al should be avoided in Mg-Ce–based extrusion alloys.     

Investigation of the Effects of Ni, Fe, and Mn on the Formation of Complex Intermetallic Compounds in Al-Si-Cu-Mg-Ni Alloys

The aim of this work is to partially substitute Fe and Mn for Ni in the 3HA piston alloy and to study the consequences through microstructural evaluation and the thermal analysis technique. Three types of near-eutectic alloys containing (2.6 wt pct Ni-0.2 wt pct Fe-0.1 wt pct Mn), (1.8 wt pct Ni-0.75 wt pct Fe-0.3 wt pct Mn), and (1 wt pct Ni-1.15 wt pct Fe-0.6 wt pct Mn) were produced, and their solidification was studied at the cooling rate of 0.9 K/s (°C/s) using the computer-aided thermal analysis technique. Optical microscopy and scanning electron microscopy were used to study the microstructure of the samples, and energy dispersive X-ray (EDX) analysis was used to identify the composition of the phases. Also, the quantity of the phases was measured using the image analysis technique. The results show that Ni mainly participates as Al₃Ni, Al₉FeNi, and Al₃CuNi phases in the high Ni-containing alloy (2.6 wt pct Ni). In addition, substitution of Ni by Fe and Mn makes Al₉FeNi the only Ni-rich phase, and Al₁₂(Fe,Mn)₃Si₂ appears as an important Fe-rich intermetallic compound in the alloys with the higher Fe and Mn contents.     

The effect of Mg on the microstructure and mechanical behavior of Al-Si-Mg casting alloys

The microstructure and tensile behavior of two Al-7 pct Si-Mg casting alloys, with magnesium contents of 0.4 and 0.7 pct, have been studied. Different microstructures were produced by varying the solidification rate and by modification with strontium. An extraction technique was used to determine the maximum size of the eutectic silicon flakes and particles. The eutectic Si particles in the unmodified alloys and, to a lesser extent, in the Sr-modified alloys are larger in the alloys with higher Mg content. Large Fe-rich π-phase (Al₉FeMg₃Si₅) particles are formed in the 0.7 pct Mg alloys together with some smaller β-phase (Al₅FeSi) plates; in contrast, only β-phase plates are observed in the 0.4 pct Mg alloys. The yield stress increases with the Mg content, although, at 0.7 pct Mg, it is less than expected, possibly because some of the Mg is lost to π-phase intermetallics. The tensile ductility is less in the higher Mg alloys, especially in the Sr-modified alloys, compared with the lower Mg alloys. The loss of ductility of the unmodified alloy seems to be caused by the larger Si particles, while the presence of large π-phase intermetallic particles accounts for the loss in ductility of the Sr-modified alloy.     

Sliding wear behavior of some Al-Si alloys: Role of shape and size of Si particles and test conditions

In this investigation, effects of the shape and size of silicon particles have been studied on the sliding wear response of two Al-Si alloys, namely, LM13 and LM29. The LM13 alloy comprised 11.70 pct Si, 1.02 pct Cu, 1.50 pct Ni, 1.08 pct Mg, 0.70 pct Fe, 0.80 pct Mn, and remainder Al. The LM29 alloy contained 23.25 pct Si, 0.80 pct Cu, 1.10 pct Ni, 1.21 pct Mg, 0.71 pct Fe, 0.61 pct Mn, and remainder Al. Wear tests were conducted under the conditions of varying sliding speed and applied pressure. The alloys were also characterized for their microstructural features and mechanical properties. The presence of primary silicon particles in the alloy led to a higher hardness but lower tensile properties. Further, refinement in the size of the primary particles improved the mechanical properties of the alloy system. The wear behavior of the alloys was influenced by the presence of primary Si particles and was a function of their size. Samples with refined but identical microconstituents (e.g., pressure cast vs gravity cast LM29 in terms of the size of primary Si particles and dendritic arm spacing) exhibited better wear characteristics. Their overall effect was further controlled by the test conditions. It was observed that test conditions leading to the generation of an optimal degree of frictional heating offer the best wear resistance. This was attributed to the reduced microcracking tendency of the alloy system otherwise introduced by the Si particles. The reduced microcracking tendency in turn allows the Si phase to carry load more effectively and impart better thermal stability to the alloy system. This caused improved wear resistance under the circumstances. Further, the primary Si particles improved the wear resistance of the alloy system (e.g., gravity-cast LM29 vs gravity-cast LM13) under high operating temperature conditions. Additional thermal stability and protection offered to the matrix by the primary Si phase, under the conditions of reduced microcracking tendency, were the reasons for the improved wear characteristics of the alloy system. Conversely, a reverse effect was produced at low operating temperatures in view of the predominating microcracking tendency. The study suggests that shape, size, microcracking tendency, and thermal stability of different microconstituents greatly control the mechanical and tribological properties of these alloys. The extent of effective load transfer between the phases plays an important role in this regard. Further, the overall effect of these factors is significantly governed by the test conditions.     

Synthesis and Characterization of Novel Chromium-Free Nickel Alloy Electrode Materials

The synthesis of two Cr-free nickel-based alloys designated as 1S with 6.5 pct Mn and 2H without Mn of compositions varying between 40 to 43.5Ni, 20Mo, 22 to 25Fe, 10Cu, 6.5 to 0Mn, 1Ti, and 0.5Al (wt pct) as filler materials for TIG welding application was performed. New filler materials were developed to reduce carcinogenic hexavalent chromium (Cr⁶⁺) fumes generated during the welding of 300 series austenitic stainless steel. The Cr-free nickel alloys were characterized for microstructure and mechanical properties. The developed alloys showed good microstructure stability in as-cast and solution-treated conditions. A material properties simulation software JMatPro predicted that 2H alloy has 2 wt pct more γ (solid solution) phase than in 1S but has 2.2 wt pct less γ′ (strengthening precipitates) phase than in 1S alloy. The tensile strength of 1S alloy was about 2.2 pct more than 2H. The solution treatment of both alloys decreased the hardness, tensile and yield strengths by about 21 pct but ductility improved by about 17 pct. Fracture studies of both alloys showed the ductile mode of failure.     

Influence of Chemical Composition of Mg Alloys on Surface Alloying by Diffusion Coating

A recently developed technique of surface alloying by diffusion-coating has been used to produce coatings on Mg alloys with various Al and Zn contents. The experimental results show that both Al and Zn solutes in the alloy promote the diffusion of alloying elements through grain refinement of the substrate alloys and through reduction of diffusion active energy because of the reduction of melting temperature of the alloys. Therefore, the efficiency of surface alloying increases by diffusion coating. Thick, dense, uniform, and continuous layers of intermetallic compounds, which consist of a τ-phase layer and a β-phase layer, can be produced on the surface of various Mg alloys. The intermetallic compound layers not only have microhardness values that are 4 to 6 times higher than the substrate but also provide effective protection of the Mg alloys from corrosion in 5 pct NaCl solution at room temperature.     

Breakdown Trade-Off Relation of Mechanical Properties via Micro-alloying in Mg–Mn Alloys

The impact of micro-alloying on tensile behavior at strain rates in various ranges is examined using five types of extruded Mg-0.3 at. pct Mn–0.1 at. pct X ternary alloys, where X is selected as a common element, Al, Li, Sn, Y or Zn. Microstructural observations reveal that the average grain size of these extruded alloys is between 1 and 3 μm, and these micro-alloying elements segregate at grain boundaries. In room temperature tensile and compression tests, these results show that the mechanical properties and deformation behavior are influenced by the micro-alloying element, even as a small addition of 0.1 at. pct. Mg–Mn–Y and Mg–Mn-Zn alloys show higher strength and smaller strain rate sensitivity (m-value) among the present alloys, owing to the rate-controlling mechanism as dislocation slip. On the other hand, the Mg–Mn–Li alloy exhibits the largest elongation to failure in tension and the highest strain rate sensitivity, associated with high contribution of grain boundary sliding to deformation. These differences are due to the grain boundary segregation of the micro-alloying elements. Compared to the common Mg alloys, the present ternary alloys also show a trade-off relationship between strength and ductility, which is similar to that of the well-known Mg alloys; however, these properties of the Mg–Mn system ternary alloys could be controlled via the type of micro-alloying elements with a chemical content of 0.1 at. pct.

     

Studies on Synthesis and Characterization of Mo Based <Emphasis Type="Italic">In Situ</Emphasis> Composite by Silicothermy Co-reduction Process

The results of an in situ synthesis of refractory metal–intermetallic composite (RMIC), Mo-16Cr-4Si (wt pct) multiphase alloy and its characterization, are presented in this study. The alloy was prepared from the oxides of molybdenum and chromium by their co-reduction with Si metal powder as a reductant. The exothermic nature of these reactions resulted in the formation of consolidated composite as a product in a single step. The thermodynamic aspects of exothermic reactions were studied by thermogravimetry/differential thermal analyzer. As-reduced alloys were remelted by arc melting and heat treated to obtain a homogenous microstructure. The evolution of phases and microstructures qA studied by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectrum analysis. The multiphase alloy consisted of Mo₃Si and discontinuous (Mo, Cr) (ss) phase with a volume percentage of 28 pct. The synthesized alloys were characterized with respect to composition, phases, microstructure, hardness, and oxidation behavior.     

Interphase boundary precipitation in liquid phase sintered W-Ni-Fe and W-Ni-Cu alloys

The microstructure of liquid-phase sintered, tungsten-based heavy alloys comprises a continuous network of spheroidal tungsten single crystals embedded in a ductile, fcc matrix phase, and the integrity of the tungsten-matrix interphase boundaries established during processing is of major importance in determining the resultant mechanical properties. A serious potential source of embrittlement in these systems involves the precipitation of a brittle third phase along these boundaries. In the present work the techniques of selected area and convergent beam electron diffraction, energy dispersive X-ray microanalysis, and scanning Auger electron spectroscopy have been used to identify the embrittling interphase boundary precipitate formed in a commercial W-4.5 wt pct Ni-4.5 wt pct Fe alloy. The interphase boundary precipitation of an intermetallic phase in a W-7.2 wt pct Ni-2.4 wt pct Cu alloy under controlled conditions of heat treatment has also been confirmed. The precipitate phase observed in the W-Ni-Fe alloy in the as-sintered furnace-cooled condition has been found to be an eta carbide with a diamond cubic crystal structure (space group Fd3m,a ₀ = 1.092 ± 0.005 nm) and a tentative composition of the form (Ni,Fe)₆W₆C, where the Ni:Fe atom ratio is approximately 2:3. Neither the carbide nor any evidence of an intermetallic phase was observed in the as-sintered, furnace-cooled W-Ni-Cu alloy, but a continuous interphase boundary film of intermetallic precipitate could be induced in specimens solution treated at 1350°C, water quenched, and aged isothermally in the temperature range 600 to 900°C. Selected area electron diffraction indicated that the phase was isomorphous with the intermetallic Ni₄W of the binary Ni-W system. This paper is based on a presentation delivered at the symposium “Activated and Liquid Phase Sintering of Refractory Metals and Their Compounds” held at the annual meeting of the AIME in Atlanta, Georgia on March 9, 1983, under the sponsorship of the TMS Refractory Metals Committee of AIME. Formerly with Department of Mechanical and Industrial Engineering and Materials Research Laboratory, University of Illinois at Urbana-Champaign     

Effects of composition and fabrication practice on resistance to annealing and creep of aluminum conductor alloys

Annealing characteristics and room temperature creep were evaluated for wire of aluminum conductor alloys Al-0.20 pct Fe (EC), Al-0.85 pct Fe and Al-0.75 pet Fe-0.15 pct Mg produced by both conventional rod fabrication and continuous rod fabrication. Throughout these studies changes in resistance to annealing and resistance to creep paralleled each other, suggesting a common mechanism for these phenomena. Increasing iron concentration from 0.20 to 0.85 pct greatly increased the number of iron-bearing intermetallic constituent particles and decreased resistance to annealing and creep. AddingMgto the high Fe alloy increased the resistance to annealing and creep. Samples from continuously fabricated rod of either EC or Al-Fe-Mg alloy had greater resistance to annealing and creep than that of conventionally fabricated samples. Transmission electron microscopic examinations revealed no precipitation of iron in the continuously fabricated rod indicating that elements in solution were retarding annealing and creep. Observations of strain aging support the hypothesis that segregation of elements to dislocations is probably the mechanism whereby creep and annealing were retarded. Formerly with Alcoa Laboratories, Alcoa Center, Pa.     

Microstructure and high-temperature tensile deformation of tiai(si) alloys made from elemental powders

Two ternary TiAl-based alloys with chemical compositions of Ti-46.4 at. pct Al-1.4 at. pct Si (Si poor) and Ti-45 at. pct Al-2.7 at. pct Si (Si rich), which were prepared by reaction powder processing, have been investigated. Both alloys consist of the intermetallic compounds y-TiAl, α₂-Ti₃Al, and ξ-Ti₅(Si, Al)₃. The microstructure can be described as a duplex structure(i.e., lamellar γ/α₂ regions distributed in γ matrix) containing ξ precipitates. The higher Si content leads to a larger amount of ξ precipitates and a finer y grain size in the Si-rich alloy. The tensile properties of both alloys depend on test temperature. At room temperature and 700 °C, the tensile properties of the Si-poor alloy are better than those of the Si-rich alloy. At 900 °C, the opposite is true. Examinations of tensile deformed specimens reveal ξ-Ti₅(Si, Al)₃ particle debonding and particle cracking at lower test temperatures. At 900 °C, nucleation of voids and microcracks along lamellar grain boundaries and evidence for recovery and dynamic recrystallization were observed. Due to these processes, the alloys can tolerate ξ-Ti₅(Si, Al)₃ particles at high temperature, where the positive effect of grain refinement on both strength and ductility can be utilized.     

Microstructure and phase identification in type 304 stainless steel-zirconium alloys

Stainless steel-zirconium alloys have been developed at Argonne National Laboratory to contain radioactive metal isotopes isolated from spent nuclear fuel. This article discusses the various phases that are formed in as-cast alloys of type 304 stainless steel and zirconium that contain up to 92 wt pct Zr. Microstructural characterization was performed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), and crystal structure information was obtained by X-ray diffraction. Type 304SS-Zr alloys with 5 and 10 wt pct Zr have a three-phase microstructure—austenite, ferrite, and the Laves intermetallic, Zr(Fe,Cr,Ni)_2+x. whereas alloys with 15, 20, and 30 wt pct Zr contain only two phases—ferrite and Zr(Fe,Cr,Ni)_2+x. Alloys with 45 to 67 wt pct Zr contain a mixture of Zr(Fe,Cr,Ni)_2+x and Zr₂(Ni,Fe), whereas alloys with 83 and 92 wt pct Zr contain three phases—α-Zr, Zr₂(Ni,Fe), and Zr(Fe,Cr,Ni)_2+x. Fe₃Zr-type and Zr₃Fe-type phases were not observed in the type 304SS-Zr alloys. The changes in alloy microstructure with zirconium content have been correlated to the Fe-Zr binary phase diagram.