H. Dieringa - Academia.edu (original) (raw)

Papers by H. Dieringa

Materials Science Forum, 2003

Creep resistant Mg alloy QE22 reinforced with maftec(R), saffil(R) or supertec(R) short fibres is... more Creep resistant Mg alloy QE22 reinforced with maftec(R), saffil(R) or supertec(R) short fibres is cycled between room temperature and 308degreesC at different ramp rates in the longitudinal and transverse directions. From the careful analysis of the strain vs. temperature thermal cycling curves true material behaviour and artifacts from the dilatometer are deciphered. From this analysis true coefficient of thermal expansion and relaxation processes are deduced. Hysteresis at higher temperatures is attributed to the relaxation process, whereas hysteresis at low temperatures giving a tilt-ground shape to the thermal cycling curves is again an artifact due to the instrument. The change in ramp rate highlights this effect. Finally, the effect of thermal cycling on microstructure is examined.

Composites Science and Technology, 2005

Short fiber reinforced AlSi12CuMgNi composites have potential applications as engine components i... more Short fiber reinforced AlSi12CuMgNi composites have potential applications as engine components in automobile industry. In these engine components, the dimensional stability is of great concern. Thermal cycling experiments can approximately simulate the real working conditions of the materials and give an evaluation of the dimensional changes during their service in the changing temperature environments. Due to the fact that in metal matrix composites the thermal strain is dependent on the phase transformation, the matrix plastic yielding and the physical damage of reinforcement, analysis of thermal strain curves could allow not only insight into their thermal expansion behavior but also into the phase transformation and possible matrix plastic deformation behavior caused by large internal thermal stresses. Compared with the thermal strain curve, the instantaneous CTE curve can clearly supply more information because it is the differential of thermal strain over temperature. It is useful to differentiate whether the appearance of a knee on the thermal strain curve is caused by the phase transformation and/or by the matrix plastic deformation, especially in metal matrix composites with age hardenable matrix. In the present paper, the aging behaviors in both the unreinforced and ceramic reinforced AlSi12CuMgNi piston alloys are investigated and discussed by analyzing the instantaneous CTE curve, DTA curve and hardness tests. The matrix plastic deformation caused by thermal stresses is discussed based on the observation of CTE divergence in the longitudinal and transverse directions. The effects of both the SiO 2 content and subsequent heat treatment on the critical temperature, above which the CTE divergence occurs, are discussed. Finally, the effects of precipitation and matrix plastic deformation on the residual strain after thermal cycling are also preliminary evaluated.

DIALOG - Materialwissenschaft und Werkstofftechnik, 2019

The Minerals, Metals & Materials Series, 2018

Newly developed die-cast alloys based on Mg–Al−Ba–Ca (ABaX) system show promise for high temperat... more Newly developed die-cast alloys based on Mg–Al−Ba–Ca (ABaX) system show promise for high temperature creep resistance. ABaX844 alloy is one of them and it has limited workability due to high alloy content. To identify the optimum processing conditions, processing map for this alloy was developed earlier, which exhibited two workability domains in the temperature and strain rate ranges: (1) 340–410 °C and 0.0003–0.005 s−1, and (2) 425–500 °C and 0.0003–0.1 s−1. Dynamic recrystallization (DRX) occurs in these domains. The map also exhibited extensive flow instability mainly at strain rates > 0.01 s−1 up to a temperature of 400 °C and at strain rates >0.1 s−1 beyond 400 °C. The aim of the present study is to validate the findings of processing map by performing forging tests in the temperature range 300–500 °C (at an interval of 40 °C) and forging speeds of 0.01, 0.1, 1 and 10 mm s−1 to produce a rib-web (cup) shape component. Finite-element (FE) simulations were performed for obtaining the variations of strain and strain rate in the components during forging. The microstructures of forged specimens deformed under optimum process conditions derived from the processing map revealed the formation of dynamically recrystallized grains. The alloy specimens forged under the conditions of flow instability have fractured and/or exhibited flow localization. The results validated the predictions of the processing map and the load-stroke curves obtained by FE simulation correlated well with the experimental curves.

Magnesium 2018, Proceedings of the 11th International Conference on Magnesium Alloys and Their Applications, 2018

International Materials Technologies and Metallurgyl Conference 2019, MTM 2019, 2019

International Journal of Hydrogen Energy, 2018

Magnesium has been studied as a potential hydrogen storage material for several decades because o... more Magnesium has been studied as a potential hydrogen storage material for several decades because of its relatively high hydrogen storage capacity, fast sorption kinetics (when doped with transition metal based additives), and abundance. This research aims to study the possibility to use waste magnesium alloys to produce good quality MgH2. The production costs of hydrogen storage materials is still one of the major barriers disabling scale up for mobile or stationary application. The recycling of magnesium-based waste to produce magnesium hydride will significantly contribute to the cost reduction of this material. This study focuses on the effect of different parameters such as the addition of graphite and/or Nb2O5 as well as the effect of milling time on the material hydrogenation/de-hydrogenation performances. In addition, morphology and microstructural features are also evaluated for all the investigated materials.

Metallische Verbundwerkstoffe, 2003

Light Metals Technology V, 2011

Aluminium is often referred to (quaintly, though sometimes disparagingly) as “solidified electric... more Aluminium is often referred to (quaintly, though sometimes disparagingly) as “solidified electricity”. By this, it is implied that we need to be cautious about aluminium and question its use since it is a very energy-intensive engineering material. Fortunately, solid aluminium and its alloys have also had good press, being highly versatile and durable in service and being readily recyclable (at about 5% of the energy required to produce the primary Al initially). However, the ground is shifting again and with the present growing focus on embodied energy and carbon footprints, aluminium’s processing and use is being revisited.

Solid State Phenomena, 2008

Magnesium alloys had gained an increasing interest in recent years due to their promising propert... more Magnesium alloys had gained an increasing interest in recent years due to their promising property profile for light weight constructions. They offer drastic advantages in weight reductions in automotive industries compared to steel or even aluminium. Therefore they can be used to decrease the emission of green house gases as requested by the EU directive for the reduction of CO 2 emissions and moreover due to their recyclability they also help to fulfill the requirements from the EU directive regarding the end of life of vehicles. But still there are some limitations with regard to strength, mostly at elevated temperatures above 130 °C. To overcome these limitations alloy development as well as process optimization has to be done for further enhancement of the range of magnesium applications. This paper will show and discuss the property profiles of the standard magnesium alloy AZ91D compared to the recently developed, heat resistant magnesium alloy MRI153. The alloys have been processed using normal high pressure die casting (HPDC), New Rheocasting (NRC) and Thixomolding ® (TM). As methods of investigation tensile and creep tests have been applied. The creep properties have been determined in the temperature range of 135-150 °C and loads of 50-85 MPa. All these trials have been accompanied by metallographic observations (light optical metallography, SEM) and density measurements to investigate the influence of the processing routes on microstructure and the porosity of the materials. It will be shown that the differences in the property profile of the chosen alloys are dependent on their different chemical compositions as well as on different microstructures that are obtained by the different processing routes. While in the case of AZ91D, TM is showing advantages compared to HPDC for room temperature applications, the NRC in combination with the heat resistant alloy leads to an improvement of creep rates by two orders of magnitudes.

Materials Science and …, 2005

The development of metal matrix composites (MMCs) is one possibility to overcome the disadvantage... more The development of metal matrix composites (MMCs) is one possibility to overcome the disadvantage of poor high temperature creep properties of present magnesium alloys. Short fiber reinforcement improves the high temperature creep resistance of magnesium alloys. ...

Scripta Materialia, 2008

... Yuanding Huang a , Corresponding Author Contact Information , E-mail The Corresponding Author... more ... Yuanding Huang a , Corresponding Author Contact Information , E-mail The Corresponding Author , Hajo Dieringa a , Norbert Hort a , Tarek Abu Leil a , Karl Ulrich Kainer a ... SEM observations show the existence of diffusive bright bands at the dendritic and grain boundaries (Fig ...

Journal of Alloys and Compounds, 2008

The AE42 magnesium alloy was developed for high pressure die casting (HPDC) from low-aluminum mag... more The AE42 magnesium alloy was developed for high pressure die casting (HPDC) from low-aluminum magnesium alloys. In this alloy the rare earth (RE) elements were shown to increase creep resistance by forming AlxREy intermetallics along the grain boundaries. The present work investigates the microstructure of squeeze cast AE42 magnesium alloy and evaluates its hardness before and after heat treatments. The

Composites Science and Technology, 2003

New magnesium alloys and composites are being developed for engine components of automobiles. The... more New magnesium alloys and composites are being developed for engine components of automobiles. The aim of developing magnesium based MMCs is not only to improve creep resistance but also to reduce the thermal expansion of the material. However, the large difference in ...

Advanced Engineering Materials, 2004

Materials Science and Engineering: A, 2017

Indirect improvement of high temperature mechanical properties of a Mg-based alloy Elektron 21 by... more Indirect improvement of high temperature mechanical properties of a Mg-based alloy Elektron 21 by addition of AlN nanoparticles, Materials Science & Engineering A,

Microstructure Control: Towards Innovative Development of Structure Materials, Summer School Lund, 2018