Optimization of chemistry and process parameters for control of intermetallic formation in Mg sludges

Intermetallic formation in sludge during magnesium(Mg)melting,holding and high pressure die casting practices is a very important issue.But,very often it is overlooked by academia,original equipment manufacturers(OEM),metal ingot producers and even die casters.The aim of this study was to minimize the intermetallic formation in Mg sludge via the optimization of the chemistry and process parameters.The Al8Mn5 intermetallic particles were identified by the microstructure analysis based on the Al and Mn ratio.The design of experiment(DOE)technique,Taguchi method,was employed to minimize the intermetallic formation in the sludge of Mg alloys with various chemical compositions of Al,Mn,Fe,and different process parameters,holding temperature and holding time.The sludge yield(SY)and intermetallic size(IS)was selected as two responses.The optimum combination of the levels in terms of minimizing the intermetallic formation were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,690℃ for the holding temperature and holding at 30 mins for the holding time,respectively.The best combination for smallest intermetallic size were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,630℃ for the holding temperature and holding at 60 mins for the holding time,respectively.Three groups of sludge factors,Chemical Sludge(CSF),Physical Sludge(PSF)and Comprehensive Sludge Factors(and CPSF)were established for prediction of sludge yields and intermetallic sizes in Al-containing Mg alloys.The CPSF with five independent variables including both chemical elements and process parameters gave high accuracy in prediction,as the prediction of the PSF with only the two processing parameters of the melt holding temperature and time showed a relatively large deviation from the experimental data.The Chemical Sludge Factor was primarily designed for small ingot producers and die casters with a limited melting and holding capacity,of which process parameters could be fixed easily.The Physical Sludge Factor could be used for mass production with a single type of Mg alloy,in which the chemistry fluctuation might be negligible.In large Mg casting suppliers with multiple melting and holding furnaces and a number of Mg alloys in production,the Comprehensive Sludge Factor should be implemented to diminish the sludge formation.

A review of magnesium die-castings for closure applications

Vehicle mass reduction in the automotive industry has become an industry-wide objective.Increasing fuel efficiency and greenhouse gas emission targets for engine-powered vehicles,and ambitions for extended range electric vehicles have motivated these reductions in vehicle mass.Mass reduction opportunities in structural automotive applications are increasingly realized through lightweight alloy castings,such as magnesium,primarily due to the ease of component substitution.The traditional benefits of magnesium die-castings including lightweighting and associated compounded mass savings,excellent strength-to-weight ratio,part consolidation,near net-shape forming,dimensional repeatability,and integration of additional components can be realized in closure applications.One recent example is the application of a magnesium die-casting for the structural inner of the liftgate in the 2017 Chrysler Pacifica,replacing nine parts in the previous generation and resulting in a liftgate assembly weight reduction of nearly 50%.The work presented here reviews past and current developments of magnesium die-castings in closure applications and discusses the benefits and challenges of magnesium alloys for these applications,including casting design,corrosion and fastening strategies,and the manufacturing design and assembly methodologies.

Recent developments in high-pressure die-cast magnesium alloys for automotive and future applications

The use of magnesium alloy high pressure die cast(HPDC)components for structural applications,especially in the automotive and transportation industries,where weight reduction is of a great concern,is increasing.As new applications are developing and existing applications are becoming more complex,there is a need for improved properties from magnesium HPDC alloys.This paper reviews the recent developments in HPDC magnesium alloys for transportation applications.Compared to the conventional HPDC magnesium alloys,i.e.AZ91D,AM50A/AM60B and AE44,these new alloys have one or more of the following properties:higher strength,higher ductility,superior high-temperature properties or higher thermal conductivities.In this work,characteristics which are important in product manufacturing or product performance will be evaluated and discussed,including die castability of powertrain component or thin-walled structural component,mechanical properties at elevated temperatures and ductility.Results indicate that these alloys have great potentials to be added to the current magnesium HPDC alloy family and being used in actual automotive and other transport applications.

Formation,characteristics and control of sludge in Al-containing magnesium alloys:An overview

Sludge consisting of heavy element phases and oxides is often generated during the casting operation of aluminum(Al)and magnesium(Mg)alloys.With the help of the well-established Sludge Factor(SF)formula,it is relatively easy to control the sludge generation in aluminum alloys.But formation mechanisms and characteristics of sludge in die casting magnesium alloys are still unclear.To ensure the production of high quality die cast components at a low cost,a full understanding of sludge in die casting Mg alloys and its proper control measures need to be developed,since excessive sludge formation affects deleteriously material and operation cost,and casting performance.In the present report,the formation,characteristics and control of Mg die-casting sludge,based on the established knowledge of sludge formation and sludge factor in Al die casting alloys,are reviewed.Previous work on characterization and assessment of sludge in die cast Mg alloys are reviewed.Metallurgical principles for control of sludge in ingot production in association with die casting of Mg alloys are discussed.Rapid assessment of Mg oxide and intermetallics relevant to sludge formation in Mg alloys are highlighted.

Exploring the concept of castability in magnesium die-casting alloys

This paper provides a summary of the recent work completed and history of the measure of manufacturability in the magnesium diecasting industry.The most popular die-casting alloys utilized in this industry are based on the Mg-Al system,including AZ91,AM60 and AM50.These are well-established alloys,and are generally considered to be highly castable.However,the concept of castability in magnesium die-casting is not a well-defined characteristic or quantitative material property.As a result,the author investigates the subject of castability for magnesium die-cast alloys and how it relates to the development of alloys for innovative applications or improved properties.This paper provides a summary of some key findings in literature on the castability of magnesium die-cast alloys,how castability is defined and evaluated,the impact of different alloying elements on the castability of magnesium alloys,and suggestions for future work.©2020 Published by Elsevier B.V.on behalf of Chongqing University.

The role of the Mg_(17)Al_(12)-phase in the high-pressure die-cast magnesium-aluminum alloy system

The Mg_(17)Al_(12)β-phase is highly influential to the performance of magnesium-aluminum high-pressure die-casting alloys. Numerous studies have investigated the effect of this phase on the room temperature and elevated-temperature mechanical properties as well as the corrosion,flammability, thermal conductivity and castability performance. This work summarizes the results of these works, as well as the studies that describe control of the Mg_(17)Al_(12)-phase through alloying additions that modify the microstructure and resulting alloy performance. The results of this work can be used as a basis for the development of alloying additions that enable modifications to the performance of high-pressure die-cast magnesium-aluminum-based alloys.