Matthias Bünck

Potential of the rheocasting process, demonstrated on different aluminum based alloy systems

This work describes the processing of different aluminum cast- and wrought alloys in the Cooling-Channel-Process. The investigations take the castability, the microstructural evolution for the SSM-processing and the resulting properties in the test specimen into account. Beside the alloys AlMg5Si2Mn (M59), AlCu4TiMgAg (AF48), AlSi12CuNiMg (SF70), AlSi17Cu4Mg (SF90), AlZnMgCu1,5 (AA7075) the optimization of the alloy AlSi7Mg0,3 (A356) by the addition of magnesium and copper were a main task of the work.

Suitability of lost cores in rheocasting process

Abstract When treated in pressure die casting processes the semi-solid aluminum alloys demand resilient cores which can bear the stress occurring during filling and the final pressure phase. The design of permanent cores is highly restricted in order to maintain removability. Lost cores provide the possibility of complex, undercut geometrical shapes which is mandatory for a variety of casting components. However, eligible materials which show appropriate resilience and proper decomposition properties at the same time, and in the upper echelon of cost-effectiveness, are seldom known. With the semi-solid process suited between HPDC and GDC regarding the core stress, several common and economically efficient lost core systems could be used. A selection of potentially suitable materials was identified and tested. The range of testing comprises widespread sand core-systems (amin-pur-coldbox and CO 2 -water-glass) as well as materials less commonly used, namely salt, plastic and zinc. Different types of conditioning are applied to enhance the surface properties. The mechanical properties of the sand cores are enhanced by different heat treatment methods during curing. The cores are tested producing a research component cast on a HPDC machine with semi-solid A356 slurry fabricated in the cooling channel process. The cast component was analyzed regarding shape stability, core removability and surface as well as the structure quality. The results show the importance of the surface conditioning for the sand-cores while salt and zinc produce good parts comparable to the reference steel core quality.

Thixocasting combination spanners using stainless steel X39CrMo17

Forging is state-of-the-art for producing hand tools on an industrial scale. Due to high demands on the stiffness and the fracture toughness, high-strength forging steels were used to provide cavity-free components with high mechanical load capacity. Moreover, forging is a cost-effective mass production process but, in spite of all its advantages, it has its limitations, e.g. in the freedom of designs. However, because of the extreme thermal loading (particularly with regard to permanent moulds) and the frequently unavoidable casting defects, hand tools are not cast. By means of thixocasting steel, technical difficulties can be reduced and new options are provided which allow the manufacturing of components with much higher complexity than that using forging. Through near-net shape production, manufacturing steps and costs can be reduced. Furthermore, steels, which are difficult to forge but nonetheless have high potential for specific applications (such as high strength or corrosion resistant steels), can also be processed. In cooperation with industrial partners, X39CrMo17 stainless steel combination spanners with 17 mm width across flats were thixocast. Forming dies were designed and optimized by simulation, the hot forming X38CrMoV5 tool steel as well as the molybdenum alloy TZM were selected as the tool alloys. The dies were treated by a plasma nitriding process and subsequently coated with crystalline Al2O3 protective coatings by plasma-enhanced chemical vapor deposition (PECVD). During the experiments, combination spanners were successfully cast in the semi-solid state. Cast parts were heat-treated to enhance the toughness of components, which was subsequently measured by a standardized torque test. Moreover, a hypothetical approach of a possible, industrial batch process was carried out using the simulation software MAGMAsoft.

Semi-Solid Casting of High-Reactive Wrought Alloys by Means of the Alloy AlLi2.1Mg5.5ScZr (AA1420*)

Semi-solid forming offers new potentials for processing of high reactive and hot crack susceptible aluminium-lithium wrought alloys. With the tailored alloy AA1420* (AlLi2.1Mg5.5 +Sc+Zr) a promising material for thixoforming with achievable high strength of up to 500MPa tensile strength and over 400MPa yield strength concomitant with its low density of 2,46g/cm3 is achievable. Due to high solid fractions the effect of solidification shrinkage could be sufficiently decreased with the result of hot-tear-free casting. Simulation supported a critical to cast automotive tie rod was exemplarily manufactured via semisolid- technology with promising results. Furthermore with an improved and advanced heat treatment enhanced mechanical properties, comparable to those of rolled AA1420, were achieved.

Properties of Thixocast Spring Steel Ratchets

Forging is state of the art for the production of hand tools in industrial scales. Due to high demands on stiffness and fracture toughness high-strength forged steels are used to provide components with high mechanical load capacity. In spite of all advantages forging is restricted by some means like the freedom of scope. However, because of the extreme thermal load and the hardly avoidable casting defects, hand tools are nowadays not cast. By thixocasting steel technical difficulties can be reduced and new options are provided, which allow manufacturing of components with much higher complexity than forging. During this work ratchets were thixocast successfully using spring steel type 61SiCr7. Based on the STC-concept, a new method to prevent the shot sleeve from damage was tested. Dies made of hot forming tool steel X38CrMoV5 were optimized by simulation and coated by plasma chemical deposition of crystalline Al2O3 protective coatings. The cast parts were heat treated successfully to enhance the toughness, which was measured by tensile and Charpy impact tests.