O.S. Es-Said

Effect of Layer Orientation on Mechanical Properties of Rapid Prototyped Samples

Abstract Abstract Tensile strength, modulus of rupture, and impact resistance were found for different layer orientations of ABS rapid prototype solid models. The samples were fabricated by a Stratasys rapid prototyping machine in five different layer orientations. The 0° orientation where layers were deposited along the length of the samples displayed superior strength and impact resistance over all the other orientations. The anisotropic properties were probably caused by weak interlayer bonding and interlayer porosity.

Design of multistep aging treatments of 2099 (C458) Al-Li alloy

Multistep artificial aging treatments coupled with various natural aging times for aluminum lithium 2099 alloy (previously called C458) are discussed to obtain mechanical tensile properties in the T6 condition that match those in the T861 condition, having a yield strength in the range of 414–490 MPa (60–71 ksi), an ultimate strength in the range of 496–538 MPa (72–78 ksi), and 10–13% elongation. Yield and ultimate tensile strengths from 90–100% of the strength of the as-received material (in the T861 condition) were obtained. The highest tensile strengths were consistently obtained with two-step, low-to-high temperature artificial aging treatments consisting of a first step at 120 °C (248 °F) for 12–24 h followed by a second step between 165 and 180 °C (329–356 °F) for 48–100 h. These T6-type heat treatments produced average yield and ultimate strengths in the longitudinal direction in the range of 428–472 MPa (62.1–68.5 ksi) and 487–523 MPa (70.6–75.9 ksi), respectively, as well as lower yield strength anisotropy when compared with the as-received material in the T861 condition.

Formation of a crater in the workpiece on an electrical discharge machine

Abstract A steel molding of ASTM A681 developed a large crater while being fabricated on an electrical discharge machine. Most probably, the fault was caused by inadequate flushing of the dielectric/coolant.

Alternative heat treatments for A357-T6 aluminum alloy

Abstract An aluminum foundry experienced frequent failures of A357-T6 aluminum castings. These failures are manifested in attaining tensile stresses and total percentage elongation below the minimum requirements of MIL-A-22180D. Sixteen heat treatments were designed to study the effect of varying the heat treatment parameters on the mechanical properties and consequently to minimize failures due to the heat treatment step.

Modeling the evolution of anisotropy in Al–Li alloys: application to Al–Li 2090-T8E41

It is widely reported in current literature that the precipitation hardened Al–Li sheet alloys exhibit extremely high anisotropy in yield (and ultimate tensile) strength, which is well beyond what can be explained as purely a consequence of the strong crystallographic texture in the material (e.g. J. Mater. Sci. Eng. A265, 1999, 100). This paper presents a crystal plasticity based modeling framework that will (i) facilitate the segregation of the contributions to the overall anisotropy from crystallographic texture and precipitation hardening, and (ii) correlate the contribution from precipitate hardening to either co-planar slip activity or the non-coplanar slip activity in the cold-working step prior to the aging heat treatment. More specifically, a Taylor-type (fully-constrained) crystal plasticity model was formulated to predict the yield strength of the fully processed sheet and its anisotropy, while accounting for the initial texture in the hot-worked sheet, its evolution during the cold-working step prior to aging, and the inhomogeneous nucleation of the T1 phase platelets (these are known to form on {111} planes, but not usually in equal amounts on the different {111} planes in a given crystal). In an effort to illustrate the methodology developed in the study, a limited set of experiments was conducted on Al–Li 2090-T8E41 alloy sheet. Off-axis stretches were applied on the sheet at room temperature prior to the aging treatment, and the mechanical anisotropy in the fully processed sheets was characterized by performing tension tests on coupons cut from the sheet at 0, 30, 45, 60 and 90° to the original rolling direction (RD). Both the initial texture in the sheet and its evolution during the different off-axis stretches were characterized. The alloys processed in this study showed pronounced anisotropy. The application of the methodology developed in this study revealed that much of the observed anisotropy in this particular data set could be explained by accounting for the texture in the sample in the processed condition. Although the data set available was inadequate to establish clear correlations of the anisotropy with preferential hardening mechanisms arising from either co-planar or non-co-planar slip activity during the off-axis stretch, there were indications favoring the latter. This case study, however, illustrates the application of the methodology developed in this study to obtain better insight into the nature of the anisotropy in these sheets and its physical origin.

The Effect of Thermal Exposure on the Mechanical Properties of 2099-T6 Die Forgings, 2099-T83 Extrusions, 7075-T7651 Plate, 7085-T7452 Die Forgings, 7085-T7651 Plate, and 2397-T87 Plate Aluminum Alloys

Aluminum alloys 2099-T6 die forgings, 2099-T83 extrusions, 7075-T7651 plate, 7085-T7452 die forgings, 7085-T7651 plate, and 2397-T87 plate were thermally exposed at temperatures of 180 °C (350 °F), 230 °C (450 °F), and 290 °C (550 °F) for 0.1, 0.5, 2, 10, 100, and 1000 h. The purpose of this study was to determine the effect of thermal exposure on the mechanical properties and electrical conductivity of these alloys. The data shows that higher temperatures and longer exposure times generally resulted in decreased strength and hardness and increased percent elongation and electrical conductivity.

The effect of off-axis thermomechanical processing on the mechanical behavior of textured 2095 Al-Li alloy

Abstract This investigation was conducted to study the influence of off-axis deformation in the thermomechanical processing on the properties of Al–Li 2095 HT72 alloy sheet. The thermomechanical processing involved several stages. First, the as-received hot rolled sheet was solution heat treated at 510°C for 30 min. Samples were then cut from the sheet and stretched off-axis at 0, 30, 60 and 90° angles (stretch axis) to the original rolling direction. All the specimens were then aged at 180°C for 24 h. Tensile coupons were then machined from each of these aged samples at 0, 30, 45, 60 and 90° (tensile axis) to the rolling direction, then tested to failure. The crystallographic texture and tensile properties of the processed samples were evaluated, and were compared to the solution heat-treated material. In the solution heat-treated condition, the material was highly textured with a very strong Brass component. Off-axis stretch followed by aging had little or no effect on the texture development of the solution heat-treated material. Upon testing, samples with stretch axis at 0° showed pronounced mechanical anisotropy; specimens tested at 45° showed about 40% drop in tensile and yield strength values when compared to those tested at 0°. However, stretching along 60° or 90° directions minimized mechanical anisotropy. The texture characteristics of all tested samples were determined and related to the changes in the mechanical properties. An attempt was made to correlate the data with some texture theories. Analysis of the results and normalization based on the Taylor’s factor showed that that crystallographic texture contributes only partly to the total mechanical anisotropy.

Effect of processing parameters on the earing and mechanical properties of strip cast type 3004 Al alloy

Electrical resistivity, superficial hardness, tensile testing, and quantitative metallography techniques were used in this study. The strip cast type 3004 aluminum alloy received sixteen different thermomechanical treatments before cups were drawn. The top edges of the drawn cups were not flat. Rather, there were high points or ears with valleys between them. The homogenization temperature varied from 510 to 621 °C at 24 h. Some samples received an additional 426 °C/24 h homogenization anneal. Most specimens were rolled along the longitudinal direction of the as-cast material, and some were rolled in the transverse direction. Most samples were recrystallized at 454 °C for 24 h in addition to the homogenization treatment. Some were recrystallized for 168 h. All samples were subsequently rolled to 0.33 mm for cup drawing and percent earing determination. The percent earing results of some samples were less than 1.5%, but the mechanical strength was also lowered. The high-temperature recrystallization anneal of 454 °C was the controlling factor in determining the earing and mechanical strength of the final rolled sheet.

Microstructure Analysis of Aluminum Alloy and Copper Alloy Circular Shells After Multiaxial Plastic Buckling

Aluminum and copper cylindrical shells were plastically buckled under quasi-static and dynamic loading conditions with an Absorption Compression-Torsion Plasticity (ACTP: Patent No. WO 2005090822) combined mechanical testing device. Optical microscopy and transmission electron microscopy (TEM) analysis were used to study the microscopic evolutions in the mechanically buckled aluminum and copper alloy samples. Optical microscopy showed evidence of the presence of second-phase particles in both the aluminum and copper alloys samples. Under dynamic loading aluminum samples showed more energy absorption as compared to copper samples. Material flow lines were more pronounced in the copper samples when observed by optical microscopy. The evidence that supports the increased energy absorption in the aluminum cylindrical shells can be supported by the TEM analysis more than the optical microscopy analysis. The TEM results showed highly oriented textured morphology with the presence of few dislocation cells structures and sub-structures.

Failure analysis of K-monel 500 (Ni–Cu–Al alloy) bolts

Abstract A bolt manufacturer used several subcontractors to fabricate K-monel 500 bolts. The completed bolts failed mechanical testing, and the manufacturer ascribed the failure to the bar stock. Testing contracted by the supplier of the bar stock showed that it met specifications. Metallographic testing described here shows that the bolts failed because of excessive grain growth and subsequent softening during heat treatment performed on the bolts after they were formed. Alternative heat treatments are discussed.