Robert Jarosz

The Microstructure of Elektron21 and WE43 Magnesium Casting Alloys after Subsequent Melting Process Operations

Magnesium alloys are one of the lightest structural metallic materials. Their specific strength and stiffness is comparable to this, characterizing aluminum alloys and even some groups of steel and titanium alloys. Their main disadvantage is low maximum working temperature (about 120°C for Mg-Al-Zn alloys). This led to development of Mg-RE-Zr alloys, which can work up to 250°C. The paper presents results of the investigations of influence of subsequent melting operations on the Elektron 21 and WE43 magnesium alloys. Elektron 21 alloy had been prepared from the pure ingots, while WE43 alloy from the scrap material. Average area of the grain flat section and eutectics volume fraction had been evaluated quantitatively. The results of the evaluation have been verified by means of Mann-Whitney U-Test and Kolmogorov-Smirnov statistical tests. The liquid metal treatment led to refinement of the grain only in Elektron 21 alloy (from Ᾱ=3559μm2 to Ᾱ=1849 μm2). Multiple modification of the WE43 alloy does not lead to further decrease of the average area of grain flat section (from Ᾱ=1638μm2 to Ᾱ=1871 μm2).

The influence of section thickness on microstructure of Elektron 21 and QE22 magnesium alloys

The paper presents analysis of section thickness’ influence on microstructure of Elektron 21 and QE22 magnesium alloys in the form of a stepped casting test. Solid solution grain size and volume fraction of eutectic areas were measured using light microscope and sterological methods. The results showed the significant increase of grain size caused by wall thickness and its slight decrease connected with the distance beetwen analysed section and the gating system. This relationship was confirmed using statistical methods. QE22 alloy demonstrated finer grain structure than Elektron 21 alloy as well as lesser susceptibility of grain size to solidification conditions

Influence of Pouring Temperature on Castability and Microstructure of QE22 and RZ5 Magnesium Casting Alloys

Magnesium alloys are widely used in automotive and aerospace industries due to their great connection of low density and good mechanical properties. They are also characterized by good castability and weldability. Their weak high temperature properties and corrosion resistance, led to development of magnesium alloys containing rare earth elements. Casting is the most popular way of manufacturing magnesium elements. However, there is a lack of investigations concerning impact of different factors on fluidity of these alloys. This paper presents results of investigations on influence of pouring temperature on castability and microstructure of QE22 and RZ5 magnesium alloys. In case of QE22 alloy, the filling length of the liquid alloy increased with the increasing pouring temperature. In RZ5 no such dependence was noted. This is probably caused by oxide films in the structure of material. Grain refinement and eutectics volume fraction also didn’t present correlation with pouring temperature.

Influence of Mould Cooling Rate on the Microstructure of AZ91 Magnesium Alloy Castings

Magnesium alloys are the lightest, widely used structural material. They are often used in aeronautical and automotive industries, where the weight savings are essential. Due to high responsibility of the elements made from magnesium alloys it is important to achieve high quality castings without any defects. The paper presents results of investigations on impact of sand mould cooling rate on microstructure and quality of the castings. Six identical castings, fed and cooled in different ways were investigated. Studies consisted of: RTG investigations and SEM and LM observations. Microstructure was evaluated qualitatively and quantitatively. RTG investigations showed that casting without feeder and cooler, casting only with feeder and castings cooled with 20mm and 40mm thick cooler contains voids inside. Castings with feeder and coolers 20mm and 400mm thick were flawless. Microstructure evaluation showed that castings with and without defects have different structure. Castings with defects were characterized by higher volume fraction of Mg17Al12 intermetallic phase. Flawless castings were characterized by fully divorced eutectic.

Influence of the wall thickness on castability and microstructure of the QE22 magnesium alloy

Majority structural elements from magnesium alloys are produced by means of casting. The big and complicated elements are mainly sand cast. The aim of the research was to investigate the influence of wall thickness on the castability and microstructure of modern magnesium alloy with RE and Ag additions – QE22. Eight 145x98mm plates have been cast for the research. Their designed thickness was equal: 0.5mm, 1mm, 1.5mm, 2mm, 3mm, 4mm, 5mm as well as 6mm. The parameters of microstructure constituents in each cast has been estimated quantitatively. The critical wall thickness, at which liquid alloy fill the mould cavity completely, is equal 4mm. With decreasing wall thickness, percentage of filled cavity is decreasing linearly. Mean area of grain flat section increased 7 times in the thickest plate (from 501μm2 to 3773μm2). The volume fraction of eutectics as well as alloy hardness decreased in the thickest plate.

The Quality of Produced Sand-cast Engine Block Made from Elektron 21 Magnesium Alloy

The casting defects, microstructure and hardness of Elektron 21 Mg sand casting alloy was investigated. Visual and radiographic examination showed the presence of non-metallic inclusions and porosity. Quantitative analysis of microstructure was performed, no correlation between section thickness, grain size, volume fraction of eutectic areas and hardness was observed. Casting defects were responsible for cracking at magnesium casting/steel tube interface.

Influence of the Pouring Temperature on the Castability and Microstructure of Elektron 21 and QE22 Magnesium Casting Alloys

Magnesium alloys are widely used in aerospace and automotive industry due to their low density, good mechanical properties and good castability. The paper presents results of the castability tests and microstructural investigations on two unmodified magnesium casting alloys, Elektron 21 and QE22. Spirals for the castability test were poured from three temperatures: 755°C, 800°C and 835°C. Volume fraction of eutectic regions and grain size in both alloys were quantitatively evaluated. Castability increased with increasing pouring temperature. Quantity of eutectics and grain size did not show straight correlation with pouring temperature.