Advanced Materials Research Vol. 1019

Abstract: Both open die and closed die powder compact forging can be used for the consolidation of Ti and pre-alloyed Ti 6Al 4V powders produced by a hydride-dehydride (HDH) process. The approach used is initial cold or warm compaction into cylindrical shapes, or into a specific pre-form shape appropriate for achieving a particular final forged shape. The economic benefit is near net-shape processing with minimum machining required after forging. Manufacturing costs are also minimised by forging a compact, with a sufficiently high enough density, in air, without a protective atmosphere. The challenge, from a manufacturing point of view, is the operation of a manufacturing route which gives rapid and qualified compaction to meet production demands and batch sintering to achieve a high enough density prior to final forging to shape. In addition to this the final product has to have the right level of mechanical properties. This paper reviews some key findings from powder compact production, through to sintering and forging. These will be presented in terms of alpha-beta phase distribution in the microstructure, the degree of porosity, heat treatment and their effects on mechanical properties.

Abstract: Microwave sintering of titanium and its alloys is a recent development in powder metallurgy of titanium. The sintering in an atmospheric pressure argon gas environment or vacuum is potentially cost effective and energy efficient compared to conventional sintering methods due to the possibility of direct microwave heating of the titanium powder via in-depth energy deposition augmented by hybrid heating in a ceramic casket. The in-depth heating permits very rapid processing (cycle times of potentially less than 10 minutes) which is intended to preserve a very fine grain structure in the final product resulting in excellent mechanical properties and the possibility of superplastic forming. We are investigating this approach using an S–Band microwave system. The process can be also used for composites, laminates, direct alloying, and functionally gradient materials. Evaluations to optimize different parameters for controlling the final density, microstructure, and properties of these materials are underway and results are discussed.

Abstract: High cost is the major reason that there is not more wide-spread use of titanium alloys. Powder Metallurgy (P/M) represents one cost effective approach to fabrication of titanium components and Additive Manufacturing (AM) is an emerging attractive PM Technique . In this paper AM is discussed with the emphasis on the “work horse” titanium alloy Ti-6Al-4V. The various approaches to AM are presented and discussed, followed by some examples of components produced by AM. The microstructures and mechanical properties of Ti-6Al-4V produced by AM are listed and shown to compare very well with cast and wrought product. Finally, the economic advantages to be gained using the AM technique compared to conventionally processed material are presented. Key words: Additive Manufacturing (AM), 3D Printing, CAD, CAM, Laser, Electron beam, near net shape, remanufacturing, Powder Bed Fusion (PBF), Direct Energy Deposition (DED)

Abstract:

Two rapid assessments of foundries in the automotive supply chain were conducted in 2012 and 2013 on behalf of the National Foundry Technology Network (NFTN), an initiative of the Department of Trade and Industry (dti). The investigation was not an academic or econometric study; but to identify areas where assistance was required by the foundries, and opportunities for growth. There are both Tier 1 and Tier 2 foundries that are qualified to, and do, supply the automotive sector. Castings, components and sub-assemblies are produced in South Africa for the majority of passenger vehicle manufactures. There has been an increase in volumes supplied by smaller, often Tier 2 & 3 foundries, however, drive train castings are largely imported. Furthermore, there was little evidence of supply contracts for the next model ranges. Local castings were said to be 10% to 30% more expensive than imported parts. Typically, sourcing discussions are made outside of the country, and price and security of supply are main considerations. Original Equipment Manufacturers (OEM’s) have committed to local sourcing, but it was clear that a significant intervention was required to change the downward trend. This would be outside the scope of both the Aluminium Federation of South Africa (AFSA) and the NFTN. It was recommended that a Competitive Improvement Initiative (CII) be launched by the NFTN. This was subsequently approved by the NFTN/dti.

Abstract: Magnesium metal is one of the few metals with multiple raw material sources. These are either from the hydrosphere of the ocean and saline lakes or from the lithosphere from ores and natural evaporites. This paper will describe CO₂ emission from both the chemical process stand-point as well as the physical process energy requirements. Present processes of electrolytic as well as the thermal reduction will be described along with their carbon dioxide emissions. Novel methods will be introduced as to how the carbon emission in the production of this light metal can be minimized in a cost effective fashion.

Abstract: Al-Mg-Si-Cu alloy 6066 is a heat-treatable wrought alloy that is commonly used in high performance bicycle frames. Wrought alloys are difficult to cast using conventional liquid casting techniques, as hot tearing can occur. However, a method that effectively reduces that risk is rheo-high pressure die casting (R-HPDC). Casting alloy 6066 using semi-solid metal processing makes it possible to be used for near-net shape forming of components. This study investigates the age-hardening response of R-HPDC alloy 6066. The effects of different solution heat treatments, natural pre-ageing and artificial ageing are studied. The different solution heat treatments investigated are a one-step and a two-step solution treatment. The one-step treatment was performed at 530°C only and the two-step treatment at 530°C followed by 550°C. It is shown that natural pre-ageing has a detrimental effect on the T6 properties and that the longer two-step solution heat treatment is justified due to an increase in hardness and prevention of incipient melting. The Vickers hardness in different temper conditions (F, T4, T5 and T6) were determined and compared to the typical hardness values of the alloy in the wrought condition.

Abstract:

This paper investigates the influence of natural pre-ageing time on T6 peak hardness of rheo-high pressure die cast (R-HPDC) 6xxx series aluminium alloys. Natural pre-ageing has a negative effect on the 6xxx series Al-Mg-Si alloys that contain higher quantities of Mg₂Si (typically > 0.90%). However, a positive effect is observed in alloys with lower quantities of Mg₂Si. The negative effect can be attributed to the clustering of solute atoms that form at room temperature because the precipitates which develop directly from clusters formed at room temperature are coarser than those developed in alloys artificially aged immediately after quenching. The opposite occurs in alloys where a positive effect of natural pre-ageing is found. The effects of the duration of natural pre-ageing on the subsequent T6 properties are of importance. In this study the T6 (190^oC-4h) hardness values of various R-HPDC 6xxx series alloys were determined after natural pre-ageing times ranging from 0h to 3240 hours. Alloys that show either the positive or the negative effect of natural pre-ageing are used. This paper also compares the influence of natural pre-ageing time on Cu-containing and Cu-free alloys. The addition of copper to the 6xxx series aluminium alloys lessens the negative effect of natural pre-ageing in the higher strength alloys.

Abstract:

This paper investigates the selection process of Al-Mg-Si-(Cu) 6xxx series alloys when used specifically for rheo-high pressure die casting (R-HPDC). The 6xxx series alloys have been developed as wrought alloys and certain factors must be taken into consideration when utilising them for semi-solid metal processing. It is shown that chemical composition has a significant effect on the solution treatment parameters that should be employed i.e. high Cu and excess Si levels necessitate the use of a two-step solution treatment to reduce incipient melting. This incipient melting is especially severe in areas within the component where liquid segregation occurs, which is a common phenomenon in R-HPDC. However, high Cu and excess Si levels also have advantages: it results in higher T6 strength and Cu-additions have been shown to minimise the negative effects of natural pre-ageing. Therefore, the composition of the alloy must be selected in such a way as to achieve acceptable strength without the dangers of incipient melting in liquid segregated areas. Another important modification of 6xxx series alloys used for R-HPDC that is presented is the addition of Ti to minimise hot tearing.

Abstract:

Semi-solid metal forming of aluminium alloys has demonstrated the capability to produce near net shaped high integrity components. Anodising of these components for aesthetic and/or improved corrosion resistance is specified by some designers or users of this technology. The corrosion behaviour of fully anodised and partially anodised A356 aluminium alloy plates produced using the CSIR Rheo-High Pressure Die Casting (CSIR-RHPDC) process was investigated using immersion testing in a 3.5% NaCl solution with pH = 7. Optical microscope equipped with image analysis software and scanning electron microscope (SEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS) were used to evaluate the behaviour of the corroded samples. The fully anodised sample showed that the anodised surface displayed some surface degradation. This degradation was more severe on the anodised surface with surface liquid segregation (SLS), but provided sufficient protection to prevent corrosion of the base metal. The partially anodised sample showed severe corrosion of the based metal with the corrosion concentrated in the silicon rich eutectic and SLS regions.