Bartłomiej Dybowski

Microstructural Phenomena Occurring during Early Stages of Cavitation Erosion of Al-Si Aluminium Casting Alloys

The researches have concerned cavitation erosion of AlSi7Mg and AlSi11Mg aluminium casting alloys. The alloys have been investigated in the as-cast condition and after the precipitation hardening. The cavitation erosion tests were performed using vibratory cavitation erosion equipment in 5 minutes. Resistance to cavitation of tested materials was estimated by means of MDE (mean depth of erosion) parameter according to ASTM G32. After the cavitation tests eroded surface of the specimens has been observed by means of scanning electron microscopy. The roughness of the surface was measured on profile contact tester. The best resistance for cavitation erosion exhibited AlSi7Mg alloy after heat treatment, the weakest AlSi11Mg alloy in as-cast condition.

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 Microstructure of AlSi7Mg Alloy in as Cast Condition

The complex microstructure of as-cast AlSi7Mg alloy has been investigated. Microstructure observations were done using light microscopy, scanning electron microscopy and transmission electron microscopy. Chemical composition of the microstructure constituents was investigated by means of energy dispersive spectrometry, conducted both during SEM and STEM investigations. Selected area diffraction was used to identify the phases in the alloy. Microstructure of the alloy in the as-cast condition consists of Al-Si eutectic and intermetallic phases in the interdendritic regions. These are: Mg2Si, α-AlFeMnS, β-AlFeSi and π-AlFeSiMg phases. What is more, number of fine precipitates were found within the α-Al dendrites. Only the occurrence of U1 (MgAl2Si2) phase has been confirmed.

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.

The Influence of Heat Treatment on the Microstructure and Mechanical Properties of the Mg-7Sn-1Si Magnesium Alloy

The influence of precipitation hardening on the microstructure and mechanical properties of the Mg-7Sn-1Si alloy is reported. It was found that the microstructure of the Mg-7Sn-1Si alloy consists of α-Mg solid solution, Mg2Sn and Mg2Si compounds. The solution heat-treatment of the tested alloy at 520 °C for 24 h causes the Mg2Sn phase to dissolve in the α-Mg matrix and spheroidization of the Chinese script Mg2Si compound. Rod-shaped and polygonal precipitates of equilibrium Mg2Sn phase were found in the microstructure after ageing treatment at 200 and 250 °C. The peak hardness is around 58 HV after 120 h at 250 °C and the hardness increment is about 22 HV. The tensile strength of the peak aged alloy is about 120 MPa. The creep rate of the Mg-7Sn-1Si alloy is of order 10−9 at a stress of 30 MPa and temperatures of 200 and 250 °C.

Properties of WE43 Metal Matrix Composites Reinforced with SiC Particles

It is well known that the properties of metal matrix composites depend upon the properties of the reinforcement phase, on the matrix and on the interface. A strong interface bonding without any degradation of the reinforcing phase is one of the prime objectives in the development of metal matrix composites. The objective of this work is to characterize the interface structure of WE43/SiC particles composite and their mechanical properties at ambient and elevated temperatures. Magnesium alloys containing yttrium and neodymium are known to have high specific strength, good creep and corrosion resistance up to 523 K. The addition of SiC ceramic particles strengthens the metal matrix composite resulting in better wear and creep resistance while maintaining good machinability. In the present study, WE43 magnesium matrix composite reinforced with SiC particulates was fabricated by stir casting. The SiC particles with 15, 45 and 250 µm diameter were added to the WE43 alloy. Microstructure characterization of WE43 MMC with 45 µm showed a relatively uniform reinforcement distribution and presence of inconsiderable porosity. Moreover, the Zr-rich particles at the particle/matrix interface were visible. The presence of SiC particles assisted in improving hardness and decreasing the tensile strength creep resistance.

Influence of Sr Addition on the Microstructure and Properties of HPDC EN AC-Al Si9Cu3(Fe) Alloy

The following paper presents results of the researches on the influence of Sr addition on microstructure and mechanical properties of EN AC-Al Si9Cu3(Fe) HPDC alloy. Two different elements were high pressure die cast for the research, one with Sr addition, second one without. Investigations involved light and scanning electron microscopy as well as hardness and tensile testing. EN AC-Al Si9Cu3(Fe) HPDC alloy microstructure is characterized by a fine dendrites of α-Al solid solution and AlSi binary eutectic mixture. What is more, many intermetallic phases are observed in the alloy. These are: α-Al15(Fe,Mn,Cr)3Si2, β-A5FeSi, A2Cu, π-A8Mg3FeSi6 and Q-Al5Mg8Cu2Si6. Sr modified alloy is characterized by a significant volume fraction of fine, fibrous AlSi-eutectic. The porosity in the modified alloy slightly decreased. Mechanical properties of the alloy increased after Sr modification.

The Porosity Description in Hypoeutectic Al-Si Alloys

Al-Si alloys are the most important group among aluminum casting alloys. They are widely used in automotive and aerospace industries. Chemical modification of the Al-Si alloys leads to formation of fine, fibrous Al-Si eutectic mixture ensuring high mechanical properties. The modification is however known to increase the alloy porosity, which may, in turn, result in decrease of its properties. The following paper presents results of the research on quantitative description of the Al-Si cast alloys porosity and influence of Na modification on the porosity of AlSi9Mg alloy. Porosity in the hypoeutectic Al-Si alloys occurs in four types: shrinkage cavities, shrinkage porosity, isolated gas pores and gas pores surrounded by shrinkage porosity. Na modification leads to increase of shrinkage pores volume fraction.

The Influence of Heat Treatment on the Microstructure and Hardness of Mg-5Si-7Sn-5Mn Alloy

The microstructure and hardness of as-cast Mg-5Si-7Sn-5Mn alloy after solution and ageing treatments is presented in this paper. It was found that the microstructure of as-cast alloy. is composed of primary dendrites crystals of Mg2Si phase, α-Mg matrix, long needle-like precipitates of Mn5Si3, Chinese script particles of Mg2Si phase and irregular Mg2Sn phase. The solution treatment at 500°C causes the dissolution of the Mg2Sn phase in the α-Mg magnesium solid solution, whereas the remaining intermetallic compounds are stable in this temperature. The hardness of alloy increases from 73 HV2 to 96 HV2 at 250°C. The increase in hardness is a result of the formation of the lath-like precipitates of Mg2Sn phase within the α-Mg matrix.