The submitted contribution addresses problems concerning influence of alloying elements (Si/Fe/Mn) of Al-Si pressure die casts (HPDC) on values of residual deformation. On the basis of results of executed experiments, mutual correlations are analyzed and described, while not only measurements results are evaluated but also metallographic outputs of obtained compounds from the view of their formation, occurrence, and size. The development of intermetallic phases structures Al(FeMn)Si as well as intermetallic ferritic phase Al3FeSi was observed. More verification experiments follow in order to apply obtained knowledge for improvement and/or preservation of casts properties on required level.
Parts manufactured by pressure die casting distinguish by suitable properties in relation to their mass. In present, these products/casts are utilized in various spheres of industries, significant share of which is automotive industry [
The paper describes basic impacts of chosen alloying elements on permanent deformation as a significant mechanical property. Mutual correlations between chosen alloying metals and resulting deformation measured on a group of casts are described. Consecutively these relations are observed during variation of content of the alloying elements in order to increase resulting strength of the cast. Providing stability in casting process is of great importance, since it has direct impact on resulting cast properties [
The quality of aluminium casts produced by pressure die casting depends closely on the content of alloying elements [
Characteristic, properties, and impact of chosen alloying elements [
Element | Characteristic |
---|---|
B | Content refines structure and increases electrical conductivity in technically clean aluminium due to precipitation of V, Cr, Mo, and Ti from solid solution |
Bi | Alloying with this element improves mechanical machinability |
Sb | It serves for improving of corrosion resistance in salty water solutions; in Al-Mg compositions decreases tendency to crack generation |
Cr | Alloying with this element decreases susceptibility of grain growth in Al-Mg alloys; in hardenable alloys it increases hardening capacity |
Cu | It decreases solidification shrinkage and enables thermal hardening; undesirable effect is a decrease in corrosion resistance; most often it is used along with Mg |
Co | In some Al-Si alloys with Fe present, it is added to transform needle-shape |
Fe | In Al-Si alloys, it occurs as an impurity; solubility in solid state is low (approx. 0.04%); due to this, it is present in structure as intermetallic compound with aluminium Al5FeSi; in Al-Cu alloys it creates intermetallic compound Al7FeCu2, thus reducing copper content in solid solution |
Mg | It is alloyed in order to increase strength properties by hardening formation of intermetallic compound Mg2Si; it deteriorates fluidity and improves machinability |
Mn | It is alloyed into aluminium alloys in order to improve strength, to increase recrystallization temperature, to refine grains, to block grain growth in the case of its segregation in form of disperse precipitates, and to suppress iron segregation in lamellar form; for elimination of harmful iron influence, it is usually added in half content of the iron content |
Mo | It is alloyed up to 0.3% in order to refine structure |
Ni | It is alloyed in order to improve strength of Al-Cu, Al-Si alloys at higher temperatures; it improves corrosion resistance |
Si | In Al-Si alloys, it is the main alloying element, presence of which improves casting properties; comparing with properties of pure aluminium, depending of silicium content, strength is increased |
Ti | It is alloyed together with B in order to refine structure |
Concentration of alloying elements in the cast is chosen according to requirements on the cast properties; however, the concentrations are limited by recommended ranges [
Iron and silicium are very often contained in aluminium alloys. Both of these elements influence mechanical properties of the casts. Theoretical knowledge shows that iron content higher than 1–1.4% has negative impact on the cast properties [
Casting machine CLH 400.01 was applied for the experimental casting. It is horizontal pressure machine with cold chamber, with manual dosing of metal. Other operations of casting process run in semiautomatic cycle, so that all conditions of casting cycle could be replicated. In semiautomatic regime of the machine with horizontal cold chamber, an operator manually scoops up metal with the scoop from the heating furnace and pours it into loading chamber. All other operations including ejection of the cast from the mould are automatic with electrohydraulic safety system for particular operations.
Set of 80 specimens were cast at a given technological order (Table
Technological order and casting parameters.
Basic pressure |
|
Path of third velocity | 270 mm |
Third velocity | 2.5 rev. |
Chamber diameter | 60 mm |
Size of pellet | 25 mm |
Temperature of meltage | 660 ± 20°C |
Insert under the chamber | 40 mm |
Dose mass into chamber | 1300 g |
Dosing scoop number | 5 |
Cycle time | 50.42 s |
Solidification time | 4 s |
Pressing time | 5 s |
Unload discharge time | 2 s |
This is a type of pressure test which follows residual deformation; the term residual deformation means deformation measured at partial unload discharge. The load is evoked by force
It holds true that
Residual deformation tests were carried out on device TIRA test 28200. Initial load force was set on value
Analysis of chemical composition was observed on spectrophotometer SPECTROLAB JR.CCD 2000. Measurements provided chemical compositions of the casts in the place of openings (A, B). The samples were detached in such a way that no thermal impacts have occurred. Surfaces were adjusted by milling technology. Shape of the samples was formed to achieve square plane with a side of 20 mm. Three measurements for every sample were carried out according to procedure for chemical composition measurements by spark erosion.
The analysis of the casts provides mass content percentage of the following elements: Si, Fe, Cu, Mn, Mg, Zn, Ni, Cr, Pb, Sn, Ti, Na, Sr, V, Zr, and Al. Table
Intervals of contents of particular elements as stated by the norm STN EN 42 4331.
Si (%) | Fe (%) | Cu (%) | Mn (%) | Mg (%) | Zn (%) | Ni (%) | Cr (%) | Pb (%) | Sn (%) | Ti (%) | V (%) | Al (%) | |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Min. | 8.00 | 0.60 | 2.00 | — | 0.05 | — | — | — | — | — | — | — | — |
Max. | 11.00 | 1.10 | 4.00 | 0.55 | 0.55 | 1.20 | 0.55 | 0.03 | 0.35 | 0.25 | 0.25 | — | — |
The results of chemical composition measurements have shown decrease in the content of observed elements in casting process. Particular casts indicate variations of the contents with decreasing tendency. The results directly correspond to the results of observation of content changes in heating furnace that are described in contributions dealing with casting process variations [
Values of chemical compositions of particular cast samples and values of residual deformation.
Sample | Si (%) | Fe (%) | Cu (%) | Mn (%) | Mg (%) | Zn (%) | Ni (%) | Cr (%) | Pb (%) | Sn (%) | Ti (%) | V (%) | Al (%) | Def. (mm) |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
A1 | 9.87 | 0.91 | 2.27 | 0.28 | 0.14 | 0.74 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 85.50 | 0.293 |
B1 | 9.88 | 0.89 | 2.31 | 0.27 | 0.13 | 0.76 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 85.48 | 0.290 |
A2 | 9.72 | 0.87 | 2.24 | 0.26 | 0.14 | 0.74 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 85.74 | 0.296 |
B2 | 9.76 | 0.88 | 2.22 | 0.27 | 0.13 | 0.74 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 85.71 | 0.292 |
A3 | 9.72 | 0.87 | 2.29 | 0.26 | 0.13 | 0.76 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 85.68 | 0.295 |
B3 | 9.51 | 0.86 | 2.2 | 0.27 | 0.12 | 0.74 | 0.06 | 0.03 | 0.11 | 0.04 | 0.03 | 0.01 | 85.99 | 0.291 |
A4 | 9.49 | 0.87 | 2.24 | 0.27 | 0.13 | 0.75 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 85.95 | 0.316 |
B4 | 9.39 | 0.85 | 2.21 | 0.25 | 0.13 | 0.73 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 86.14 | 0.313 |
A5 | 9.41 | 0.83 | 2.24 | 0.25 | 0.13 | 0.74 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 86.08 | 0.312 |
B5 | 9.48 | 0.85 | 2.24 | 0.25 | 0.13 | 0.74 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 86.00 | 0.311 |
A6 | 9.3 | 0.82 | 2.19 | 0.25 | 0.14 | 0.76 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 86.20 | 0.327 |
B6 | 9.47 | 0.85 | 2.21 | 0.25 | 0.14 | 0.76 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 86.02 | 0.305 |
A7 | 9.49 | 0.85 | 2.22 | 0.24 | 0.13 | 0.75 | 0.06 | 0.03 | 0.12 | 0.04 | 0.03 | 0.01 | 86.03 | 0.316 |
B7 | 9.41 | 0.83 | 2.16 | 0.25 | 0.13 | 0.75 | 0.06 | 0.03 | 0.11 | 0.04 | 0.03 | 0.01 | 86.19 | 0.306 |
A8 | 9.32 | 0.81 | 2.25 | 0.22 | 0.13 | 0.75 | 0.06 | 0.02 | 0.12 | 0.05 | 0.03 | 0.01 | 86.23 | 0.334 |
B8 | 9.28 | 0.83 | 2.24 | 0.23 | 0.13 | 0.75 | 0.06 | 0.02 | 0.12 | 0.05 | 0.03 | 0.01 | 86.25 | 0.338 |
A9 | 9.34 | 0.81 | 2.28 | 0.22 | 0.13 | 0.75 | 0.06 | 0.02 | 0.12 | 0.05 | 0.02 | 0.01 | 86.19 | 0.331 |
B9 | 9.23 | 0.79 | 2.21 | 0.23 | 0.13 | 0.76 | 0.06 | 0.02 | 0.12 | 0.05 | 0.03 | 0.01 | 86.36 | 0.336 |
A10 | 9.44 | 0.81 | 2.25 | 0.23 | 0.13 | 0.75 | 0.06 | 0.03 | 0.12 | 0.05 | 0.03 | 0.01 | 86.09 | 0.33 |
B10 | 9.32 | 0.8 | 2.24 | 0.22 | 0.13 | 0.73 | 0.06 | 0.03 | 0.12 | 0.04 | 0.04 | 0.01 | 86.26 | 0.323 |
From measurements of the chemical composition of each sample (Table
On the basis of the analysis, it was suggested to stabilize or slightly increase iron content and to directly increase manganese content. An iron content should be up to one percent because—as it is given in the theory and also prescribed by the norm—exceeding of iron content above 1.4% causes strong negative effects [
The experiment that followed was based on suggested iron and manganese content values. The set of casts was produced with the same methodology as in previous case. Six casts from the set were selected for residual deformation and chemical composition analyses. Obtained values are shown in Table
Obtained content values of chosen elements (Si/Fe/Mn) of particular samples of the casts and values of residual deformation after content correction of Fe-Mn.
Sample | Si (%) | Fe (%) | Mn (%) | Def. |
---|---|---|---|---|
A11 | 9.5 | 0.95 | 0.35 | 0.284 |
B11 | 9.58 | 0.98 | 0.35 | 0.282 |
A12 | 9.26 | 0.94 | 0.35 | 0.287 |
B12 | 9.46 | 0.96 | 0.34 | 0.284 |
A13 | 9.22 | 0.91 | 0.3 | 0.29 |
B13 | 9.34 | 0.94 | 0.34 | 0.29 |
A14 | 9.18 | 0.94 | 0.32 | 0.293 |
B14 | 9.3 | 0.93 | 0.32 | 0.293 |
A15 | 9.07 | 0.91 | 0.31 | 0.294 |
B15 | 9.24 | 0.91 | 0.31 | 0.296 |
A16 | 9.06 | 0.87 | 0.3 | 0.296 |
B16 | 9.17 | 0.86 | 0.3 | 0.298 |
Dependence courses of particular casts on chemical composition on casting order of the casts are given in Figure
Values of chemical composition (Si/Fe/Mn) for the experiments.
In this part, dependence courses of residual deformation on chemical composition of the casts are observed. Particular influences of chosen alloying elements are given in introductory part of the paper. An influence of iron and manganese on resulting residual deformation was observed, at the same time, a possible influence of silicium content variation was evaluated. Considering that Si influences fluidity, all observed casts were X-ray tested, and no internal defects were detected. Also, visual and dimensional inspections did not show any negative changes of the casts. Figure
Dependence courses of residual deformation on change of Fe and Mn content.
For increasing values of iron content, it is possible to see the decrease of residual deformation values (Figure
Figure
Dependence of permanent deformation on iron and manganese.
From the analysis of microscopic images, it follows that structures of A1, A2, B1, and B2 samples (Figure
Metallographic images of boundary casts.
More massive structural zones of ferritic phase Al3FeSi have negative effects on values of residual deformation, while they are compensated by increasing manganese content which causes refining of Al3FeSi phase and formation of intermetallic Al(FeMn)Si phases. These structures are more beneficial in terms of exposure to residual deformation.
In the case of manganese, it is necessary to observe the correlation, because if it is not saturated, and it is eventually deposited as a thermal compound AlMnSi.
Realized experiments and discussions show several important aspects of obtained and verified knowledge. Experiments were focused on a group of three elements (Si, Fe, and Mn) occurring in subeutectic Al-Si alloy. Selection of the group was based on knowledge of realized measurements obtained within monitoring of processes in heating furnaces, where variations of elements concentration have been observed. The variations relate to silicium, iron, and manganese, all in decreasing trends.
Described results also show that in casting process, concentration variation of silicium, iron, and manganese may occur, whilst these variations in the conditions of real experiment have reached values for Fe 15%, for Mn 27%, and for Si 7%. Also, an influence of these variations on values of residual deformation was confirmed; theoretical approach was proved. The change of deformation in such a case is 16% from observed interval. At the same time, it is possible to evaluate correlation coupling of Si/Fe/Mn with regard to the metallographic tests results.
From verification measurements and from overall behaviour of particular ingredients, it can be concluded that even though the iron is an impurity, it can be used to increase compression strength for loads in incomplete unload discharge. The mean deformation value of standard meltage presents value 0.313 mm with standard deviation 0.0163 and variance of residual deformation
Taking into account the variations of alloy content comparing to commercial alloys, it is possible to ensure alloying elements content increase during melting process by subsidizing the particular ingredients or by proper combination of recurrent material.