EP0400059B1 - Cast aluminium alloys - Google Patents

Cast aluminium alloys Download PDF

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Publication number
EP0400059B1
EP0400059B1 EP89902718A EP89902718A EP0400059B1 EP 0400059 B1 EP0400059 B1 EP 0400059B1 EP 89902718 A EP89902718 A EP 89902718A EP 89902718 A EP89902718 A EP 89902718A EP 0400059 B1 EP0400059 B1 EP 0400059B1
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alloy
level
present
cast
particles
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English (en)
French (fr)
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EP0400059A4 (en
EP0400059A1 (en
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John Alan Eady
Christopher John Heathcock
Peter Lawrencer Kean
Kevin Phillip Rogers
Rodney Alan Legge
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Rio Tinto Aluminium Ltd
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Comalco Aluminum Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
    • C22C21/04—Modified aluminium-silicon alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
    • C22F1/047—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with magnesium as the next major constituent

Definitions

  • This invention relates to high strength, wear resistant Al-Si alloys of improved castability, and to a method of improving the castability of such alloys.
  • the alloys of the invention are suitable for complex permanent mould castings and sand castings in which it generally is difficult to avoid the formation of excessive primary Si.
  • the invention provides simple to utilise chemical means for controlling the formation of primary Si in such castings.
  • the Jenkinson alloy has preferred additions of at least one of Cu and Mg, and modified by at least one of Sr and Na.
  • the Jenkinson alloy is the subject of Australian patent 475116 and corresponding patents in other countries comprising: British 1437144 Swedish 7468645 Canadian 1017601 United States 4068645 French 2225534 West Germany 2418389 Japanese 50116313
  • the Jenkinson alloy more specifically has the composition by weight: Si 11-20% Mg 0-4% Cu 0-4% Fe 0-1.5% Sr 0-0.10% Na 0-0.10% the balance, apart from unavoidable impurities, being Al.
  • a melt of that composition is allowed to solidify under conditions such that the growth rate R of the solid phase is 10 to 5000 ⁇ m/sec and the temperature gradient G at the solid/liquid interface is from 100° C/cm to 500° C/cm.
  • Such solidification conditions are controlled to produce the Jenkinson alloy with a microstructure that is virtually free from primary Al or Si phases, containing not less than 90% Al/Si eutectic phases where the Si is in the form of eutectic particles of less than 10 ⁇ m in diameter, and preferably less than 1 ⁇ m diameter.
  • the eutectic coupled growth concept was proposed to achieve a fully modified eutectic structure.
  • Such a structure can be achieved under the above-indicated, strictly controlled solidification conditions, such as in a laboratory solidification rig or in very simple castings.
  • it has proved to be impossible to obtain structures substantially free from primary Si in complex castings (such as cylinder beads and engine blocks) produced with that alloy by conventional casting techniques.
  • the presence of primary Si greatly reduces the properties of the alloy, especially machinability and fatigue resistance.
  • 3HA alloy a complex Al-Si alloy with a lower Si range of 12-15%.
  • Our 3HA alloy is the subject of Australian patent 536976 and corresponding patent protection in other countries comprising: British 2085920 New Zealand 198294 Canadian 1175867 Swedish 454446 French 2489846 United States 4434014 Japanese 62011063 West Germany 3135943
  • Our 3HA alloy has the following composition by weight: Si 12-15% Cu 1.5-5.5% Ni 1.0-3.0% Mg 0.1-1.0% Fe 0.1-1.0% Mn 0.1-0.8% Zr 0.01-0.1% Si modifier 0.001-0.1% Ti 0.01-0.1% the balance, apart from impurities, being Al.
  • the proposal for the 3HA alloy typically entails preparation by establishing a melt of that composition and allowing the melt to solidify under conditions such that during solidification R is from 150 to 1000 ⁇ m/sec and G is such that the ratio G/R is from 500 to 8000 Cs/cm2.
  • the 3HA alloy is much improved, compared with the Jenkinson alloy, in respect of its foundry, tribological and mechanical properties.
  • the 3HA alloy can be cast successfully by high pressure die casting operations for both simple and complex casting shapes and such casting operations are suitable for use on a production basis for that alloy.
  • the 3HA alloy also can be cast successfully on a production basis in sand and permanent moulds, and castings having good properties can be produced.
  • casting of the 3HA alloy in sand or permanent moulds on a production basis essentially is limited to castings of relatively simple shapes, such as cylindrical components. With more complex castings produced in sand or permanent moulds, tight controls are necessary to avoid excessive formation of primary Si, typically as large particles.
  • the structure of 3HA alloys can be improved in complex castings by the judicious application of cooling/heating in permanent moulds or of chills in sand moulds.
  • these techniques can be costly in the high volume production of complex castings such as engine blocks and cylinder heads. Consequently, the problem of structure control limits the practical utility of the 3HA alloy, despite the highly desirable characteristics able to be obtained with that alloy in simple castings or those produced by high pressure die casting.
  • the present invention is directed to overcoming the foregoing problems by providing an improved method of casting hypereutectic Al-Si alloys.
  • the invention is particularly concerned with achieving alloys of the 3HA type which have improved castability and provides techniques particularly useful in the production of hypereutectic aluminium alloys having from 12 to 15% Si, with all compositions herein being on the basis of percent by weight.
  • the alloys of the present invention may be, apart from the amount of strontium, broadly such as disclosed in our Australian patent specification 536976 and its counterparts in other countries, subject to qualifications specified herein, but are not limited to the alloys of that specification.
  • the invention comprises the addition to the Al/Si alloys of abnormally high levels of strontium, compared with those conventionally used, in combination with titanium.
  • hypoeutectic Al-Si foundry alloys (containing less than 12.7%Si) commonly use very low levels of modifier such as Sr (0.03%) to refine and round the eutectic Si particles.
  • Sr modifier
  • hypereutectic alloys (containing greater than 12.7% Si) the use of modifiers such as Sr up to 0.1% has been proposed to extend the coupled zone and thus extend the Si content of the alloys over which substantially eutectic microstructures can be achieved, such as disclosed in said specification 536976.
  • modifiers have been used at these quite low levels to avoid adverse effects.
  • the level is below 0.10%, as an intermetallic compound, detrimental to mechanical properties, forms beyond 0.10%. Particles of the intermetallic compound form as platelets which create points of weakness in the microstructure, resulting in a reduction in strength and fatigue resistance.
  • Sr as the modifier, this is illustrated by the reports of G.K. Sigworth, Research Report 83-12 Nov., 1982, Cabot Corporation, P.O. Box 1462, Reading PA., 19603 and B. Closset and J.E. Gruzleski, AFS Transactions, 82/31, pages 453-464.
  • the beneficial effects of the level of Ti in the high Sr containing Al-(12-15%) Si alloys of the present invention are also unexpected.
  • Levels of Ti (0.03 - 0.05%) are commonly used in aluminium foundry alloys as a grain refiner, providing nucleating sites for primary aluminium. In the present invention, however, we have found that the addition of Ti at a level in excess of 0.005% to the high Sr-containing alloy has other, unexpected, beneficial effects.
  • Ti in excess of 0.005% has been found to provide a first beneficial effect in further suppressing the formation of primary Si particles, but only in the high Sr-containing alloys.
  • the use of Ti in the alloys according to the invention achieves a second beneficial effect.
  • This effect is of preventing the formation of detrimental Sr intermetallic platelets which would be expected to result with use of Sr at a level in excess of 0.10%.
  • the use of Ti in excess of 0.005% according to the invention is found to result in those particles being present in a substantially equi-axial, blocky form. That is, the Ti in this case is found to change the morphology of the Sr intermetallic particles.
  • the combined result of Sr at a level in excess of 0.10% and Ti at a level in excess of 0.005% can be such that the alloy according to the invention can be substantially free of primary Si particles, while flotation of such particles as do form is substantially prevented.
  • the Ti most preferably is added as AlTiB without excess boron, or as AlTi master alloy, which contains or provides at least one compound such as (Al,Ti)B2, TiB2 and TiAl3 . Also, other similar compounds such as TiC and TiN can achieve the same effects as the above compounds. In each case, the addition of at least one of the Ti compounds is such as to achieve a Ti level in excess of 0.005%. Whenever a Ti addition is referred to hereafter it should be read as indicating the addition of at least one of the above compounds unless specified otherwise.
  • the invention also provides a cast hypereutectic Al-Si alloy with from 12-15% Si, the alloy having good wear resistance and machinability, improved fatigue strength and good levels of ambient and elevated temperature properties; wherein said alloy comprises the features of claim 19.
  • the present invention is based on the combination of unexpected discoveries that beneficial results can be achieved in Al-(12-15%) Si alloys by the use of particular levels of Sr and Ti.
  • Sr at a level of from 0.11% to 0.4% in combination with Ti in excess of 0.005%, as specified, provides the ability to substantially increase the utility of hypereutectic aluminium alloys having from 12-15% Si in the commercial production of castings. That is, by appropriate use of that combination of Sr and Ti, it becomes possible to produce castings in which both primary Si is suppressed and formation of Sr intermetallic platelets virtually eliminated.
  • the extent to which suppression of primary Si is necessary varies with the variability in solidification conditions, and hence the complexity of casting.
  • the tendency for primary Si to be formed is greater for a given casting made in a sand mould compared with a permanent mould.
  • each of these matters can be compensated for by appropriate adjustment of the lower level of Sr addition, and with corresponding additions of Ti for further control of primary Si and control of Sr intermetallics.
  • Sr is present at a level of at least 0.11% and this is suitable for castings of a lower degree of complexity or of relatively thin wall section produced in a permanent mould or for relatively simple or thin wall section castings produced in a sand mould.
  • the level of Sr need not exceed 0.4%, as additions of Sr above 0.4% are found not to achieve any beneficial increase in respect of suppressing formation of primary Si and thus simply increase the tendency for the formation, and difficulty in control, of Sr intermetallics.
  • the range of Sr addition is from 0.11 to 0.4%, with 0.15 to 0.4% being preferred.
  • Sr at a level of 0.18 to 0.4% is more preferred, with 0.25 to 0.35% being most preferred.
  • the level of Ti required in the high Sr-containing alloy is in excess of 0.005%.
  • the Ti level should not exceed 0.1% Ti since, above this level, it has a negative consequence and appears to increase primary Si formation.
  • the optimum level can be different and for example, with TiAl3 as in Al-Ti master alloy, the Ti level should not exceed 0.25%.
  • the level of Ti required is dictated in part by, and generally increases with, the level of Sr.
  • Ti is provided at a level of 0.01% to 0.06%, most preferably from 0.02% to 0.06%, such as from 0.03% to 0.05%.
  • the Ti compounds can be added in different forms and ways including master alloy as waffle, briquettes, rod or powder or as individual compounds in powder form.
  • the powders can be added by flux injection techniques.
  • the use of Sr at a level of from 0.11% to 0.4%, in addition to reducing the number, and preventing flotation, of primary Si particles, can also provide the known modifier effects in the alloys of the present invention. That is, the Sr can modify (refine and round) the shape of the eutectic Si particles and extend the Si content of the alloys with substantially fully eutectic microstructures.
  • the alloys of the invention if required, also can include Na, a known modifier for this latter purpose.
  • such known modifier if present, is used within its normal range of up to 0.01%, and is additional to the use of Sr. Excess levels of Na by itself will not have the desired effect.
  • the alloy and method of casting have been defined in terms of its Si, Sr and Ti content, as well as other alloying additions present.
  • the additions of Cu, Ni, Mg, Fe, Mn and Zr are to provide strengthening and hardening intermetallic compounds.
  • melt and alloy of the invention can include Zn, Sn, Pb and Cr. These elements, in general, do not confer a significant beneficial effect but also do not have adverse consequences where used below the respective limits specified above; although, if present, they should not exceed these limits to avoid adverse consequences.
  • each of Ca and P preferably is at a level not exceeding 0.003%.
  • the present invention can be used in combination with this process to enable the problem of formation and floating of such large primary Si particles to be overcome even more positively.
  • an improved type of alloy 3HA and such process for its production based on such specific cooling conditions.
  • the higher levels of Sr with Ti again reduce the number, and substantially prevent flotation, of the primary Si particles.
  • This preferred form can, of course, be used with other than relatively complex castings. However its application principally is in relation to such complex castings in which it is otherwise virtually impossible to eliminate primary Si particles and if they occur, their flotation, because of the variation in solidification conditions that can occur in such castings, for example when there is a combination of very thin and very thick sections.
  • Ti is found not to achieve an additional benefit in changing intermetallic morphology but has a tendency to increase primary Si formation.
  • the composition of the alloy requires the careful selection of these alloying elements and the correct proportions of each to achieve optimum benefit. In most cases the effect of one element depends on others and hence there is an interdependence of the elements within the composition. In general, levels of these alloying elements above the maxima specified for the alloys of the invention give rise to excessively coarse primary intermetallics. Levels below the minima specified in general do not achieve the practical useful effect detailed in the following.
  • Cu, Ni, Mg, Fe, Mn and Zr provide intermetallic compounds which form part of the eutectic microstructure and are based principally on the Al-Si-Cu-Ni system.
  • the eutectic intermetallic particles are principally silicon but Cu-Ni-Al, Cu-Fe-Ni-Al and other complex intermetallic phases also may be present.
  • the intermetallic particles comprising the eutectic must be fine (less than 10 ⁇ m in diameter), preferably uniformly dispersed and preferably with an inter-particle spacing not greater than 5 ⁇ m.
  • the alloys of the invention comprise a dispersion of intermetallic precipitates within the alpha aluminium phase of the eutectic. Such dispersion reinforces the matrix and helps the loads to be transmitted to the eutectic particles and increases the ability for load sharing if any one eutectic particle cracks.
  • the elements Mg and Cu are responsible for strengthening the matrix by precipitation hardening and/or the formation of solid solutions.
  • the Cu to Mg ratios are preferably within the limits of 3:1 to 8:1. Below this ratio unfavourable precipitates may form. Cu levels beyond the specified limits may reduce the corrosion resistance of the alloy in some applications.
  • Strengthening is further enhanced by the presence of stable Mn and/or Zr containing dispersed particles. We also include these elements to improve high temperature resistance.
  • Ni, Fe and Mn are particularly effective for improving elevated temperature properties and form a number of compounds with each other. These elements are interchangeable to a certain degree as shown below: 0.2 ⁇ Fe + Mn ⁇ 1.5 1.1 ⁇ Fe + Ni ⁇ 3.0 1.2 ⁇ Fe + Ni + Mn ⁇ 4.0 Alloys of the invention may therefore be primary alloys with the lower Fe content or secondary alloys where the Fe levels may reach the maximum of the specification. The Mn and Ni content must be adjusted accordingly.
  • Titanium is a well known grain refiner and as a result can improve the mechanical properties of the alloy, in addition to its role detailed herein in further decreasing the number of primary Si particles formed and in changing the morphology of any Sr intermetallic particles so that platelets are not formed.
  • the compositions are such that most properties can be improved by heat treatment. It is understood, however, that heat treatment is optional.
  • the cast alloy may be directly subjected to a stabilising artificial ageing treatment at 160-220°C for 2-16 hours.
  • a variety of other heat treatment schedules may be employed and may include solution treatment at 480-530°C for 5-20 hours. These solution treatments are selected to provide a suitably supersaturated solution of elements in Al, whilst still avoiding unacceptable growth of the strengthening intermetallic particles so that a preferred dispersion of eutectic particles remains, i.e. a microstructure in which the eutectic particles are less than 10 ⁇ m in diameter, preferably equiaxed, preferably uniformly dispersed and preferably with an interparticle spacing not greater than 5 ⁇ m.
  • the solution treatment may be followed, after quenching, by artificial ageing at 140-250°C for 2-30 hours.
  • a typical heat treatment schedule may be as follows: 8 hours at 500°C; quench into hot water; artifically age at 160°C for 16 hours.
  • the process for 3HA alloy as disclosed in said specification 536976 requires that the temperature gradient, G, be in the range of 7.5°C/cm to 800°C/cm and the growth rate, R, be in the range of 150 ⁇ m/sec to 1000 ⁇ m/sec giving a G/R range of 500 to 8000°Cs/cm2.
  • the alloy of the present invention is suitable for castings solidifying under temperature gradients of less than 7.5°C/cm and growth rates of less than 150 ⁇ m/sec.
  • the lower limits for G and R applicable to the alloy of this invention are estimated to be close to 0°C/cm for G and as low as 15 ⁇ m/sec for R.
  • castings can be produced in which microstructures are controlled essentially by chemical means, allowing use of a significantly wider range of solidification conditions, and thereby eliminating the need for reliance on stringent control over solidification conditions.
  • castings with the desired microstructure can be produced using conventional sand moulds, even in the case of castings featuring pronounced varying section thicknesses.
  • Ti and B are commonly used in Al-Si alloys, to which they are added in the form of Al-Ti-B alloy, to provide particles which act as nuclei for aluminium grains during solidification such that a finer grain structure is achieved. While most alloy specifications allow Ti levels up to 0.2%, in practice the levels normally are kept below 0.05% because excess TiB2 can lead to castings having hard spots (clusters of TiB2 particles). Such hard spots or clusters create machining problems. Unexpectedly, in the alloys of the present invention, such clusters are not present to any adverse extent. Boron levels are not usually specified in Al-Si alloys; rather they are determined by the B content of the Al-Ti-B alloying addition but generally do not exceed 0.05%.
  • the use of Ti in excess of 0.005% in the high Sr-containing alloy, according to the invention appears to act in a quite unexpected manner in both further reducing the number of primary Si particles formed and in preventing formation of Sr intermetallic platelets. That is, the conventional role of Ti is in nucleating Al grains. In contrast, in the present invention, the Ti discourages the formation of primary Si particles and changes the morphology of the Sr intermetallic particles, rather than just nucleating further, finer platelike particles. It is therefore not a simple case of Ti providing more nucleating sites for the Sr intermetallic platelets to form, but rather of some more complex mechanism operating which can discourage primary Si formation and change the crystallographic growth kinetics of the Sr intermetallic particles.
  • the Sr can be added or adjusted to a required level of from 0.11% to 0.4% in a melt to form an ingot of the alloy of the invention, or just prior to carting of products from a melt.
  • the addition of Sr is possible in a melting furnace, a holding furnace or in a launder.
  • the Ti compounds also can be added to a required level such that Ti is in excess of 0.005% up to its specified levels at one or other of those stages.
  • the alloy of the invention is characterised by several beneficial properties. These are because of its special microstructure which is substantially free of primary silicon particles and those that are there do not float, and which contains substantially no Sr intermetallic platelets.
  • the alloy of the invention has good machinability similar to that of the alloy of patent 536976 when the latter alloy is able to be cast to give the correct microstructure
  • the machinability of the alloy of the present invention is much more consistent as a consequence of its more consistent microstructure. This, of course, is in keeping with the control by chemical means over the formation of primary Si particles.
  • the alloy of the present invention exhibits significantly enhanced fatigue strength compared with the alloy of patent 536976. Also, while tensile strength can be slightly, but not significantly, reduced compared with the alloy of patent 536976, other physical properties such as hardness and resistance to wear are essentially the same as for the alloy of that patent.
  • the alloy of the present invention while equivalent in some respects to that of patent 536976, is superior in that it is characterised by important improvements in castability, which provide consistent microstructures and hence excellent machinability and fatigue strength. These improvements enable more practical, high volume casting on a production basis, thereby extending the range of products able to be cast on such basis, and also achieving products having a wider range of practical utility.
  • alloys in which the microstructure is predominantly eutectic can contain up to 10% of primary alpha-aluminium dendrites. We have found that dendrites to such level can be tolerated without excessive decrease in properties of the alloy. With progressive increase of other alloying additions producing intermetallic particles, the matrix exhibits eutectic cells bounded by such intermetallics, although the eutectic still predominates.
  • Figures 1 to 3 in their respective photomicrographs (a)x50 and (b)x 100, illustrate clearly the constraints on the alloy and method disclosed in the Australian patent 536976.
  • the photomicrographs are taken from castings made from a typical 3HA alloy according to that patent and containing Sr as the modifier at a level below 0.1% and cast under varying conditions.
  • the G and R values for the casting in Figure 1 would be in the ranges specified for theses parameters for 3HA alloy, whereas the G and R values for the castings in Figures 2 and 3 would be below the lower limits specified for these parameters for 3HA alloy; specifically G would be in the range 1-5°C/cm and R in the range 10-30 ⁇ m/sec.
  • Figure 1 shows an optimum structure of a relatively simple permanent mould casting of that typical alloy.
  • Figures 2 and 3 show non-optimum structures respectively from a sand mould cast finned cylinder and an engine block of that typical alloy.
  • Each of the castings of which the structure is shown in Figures 2 and 3 contains substantial numbers of large primary Si particles.
  • the matrix since the formation of primary Si evident in Figures 2 and 3 has depleted the matrix of Si, the matrix in each case features large areas of alpha-aluminium in dendrite form and unmodified Al-Si eutectic.
  • FIG. 3 adjacent to the photomicrographs (a) to (c) of Figure 3, there is provided a wall-section representation of the engine block, with designations (a) to (c) of the representation having the same relevance.
  • the engine block was cast in the orientation shown, with a melt flowing upwardly in the mould from below, after which the mould was inverted for solidification of the melt. Parts of the wall section thickness were such that a poor microstructure was obtained throughout the regions of the section.
  • Figure 5 shows the cycles to failure at 300 MPa applied stress for a test casting having an optimum structure as in Figure 1, substantially free of primary Si, as contrasted with test castings having non-optimum structures as in Figure 2 or 3 and respective levels of primary Si.
  • the castings were cast under conditions attempting to provide a G/R ratio throughout the casting of from 1000 to 2000°Cs/cm2.
  • the low cycle fatigue data of Figure 5 illustrates the dramatic reduction of fatigue strength attributable to primary Si.
  • the importance of structure, including the presence or absence of primary Si, is further highlighted by Table 5 of Example 3 and Table 7 of Example 4 of patent specification 536976. Small deviations from optimum structure result in substantial reductions in resistance to compressive fatigue and sliding wear. Consistent microstructures, as can be achieved by the current invention are therefore crucial.
  • the present invention provides a chemical method for widening the range of necessary solidification conditions and controlling microstructure, thereby eliminating the need for such stringent control over solidification conditions.
  • Sr at a level of from 0.11% to 0.4% with Ti in excess of 0.005% up to its specified levels is used in a novel manner to ensure formation of substantially fully eutectic microstructures.
  • the addition of high levels of Sr has been found to have beneficial effects on the structure of Al-(12-15%) Si alloys.
  • Sr has the effect of preventing the flotation and reducing the number, but not eliminating, primary Si particles formed during solidification; this resulting in a uniform dispersion of relatively coarse Si particles throughout the casting.
  • This is illustrated in the photomicrograph (x50) of Figure 7(a), for a 3HA type of alloy containing 0.3% Sr, and no Ti additions.
  • the use of a higher level of Sr according to the invention has prevented flotation and reduced the number of the primary Si particles; those particles being relatively coarse, but evenly distributed through a substantially fully eutectic matrix.
  • the same structure also features Sr intermetallics in platelet form.
  • the scanning electron photomicrograph (x150) and x-ray analysis of Figure 8 is taken on a fracture surface of the same alloy as shown in Figure 7(a) and (b).
  • the photomicrograph of Figure 8 shows the Sr intermetallic platelets in the fracture surfaces, while the x-ray spectrum shows those particles to consist mainly of Al, Si and Sr.
  • Figure 9 shows the effect of increasing Sr content in a 3HA type alloy from the conventional level below 0.1%, through the range of up to 0.4% required by the present invention.
  • Tensile strength falls progressively from about 370 MPa to about 265 MPa over those ranges, due to the detrimental effect of the increasing content of Sr intermetallic compounds in the form of platelets.
  • this adverse effect is, as previously described, accompanied by the beneficial effect of achieving a uniform dispersion of primary Si, with this beneficial effect providing a significant improvement for the purpose of many applications.
  • the tensile strength curve of Figure 9 is drawn through asterisk points for alloy substantially free of Ti.
  • a point shown by a circle, which is the average of multiple tests. That point is for 0.30%Sr, in combination with 0.05%Ti added as Al-5%Ti-1% B, according to a preferred form of the invention.
  • the point illustrates the beneficial effect of the addition of Ti, in combination with the higher level of Sr, in further reducing the amount of primary Si and, in particular, in changing the morphology of the Sr intermetallic particles and preventing their formation as platelets and hence achieving restoration of tensile strength.
  • the Ti addition illustrated can be (Al,Ti)B2, TiB2, TiAl3, or a similar compound.
  • the component depicted in Figure 10 was cast under conditions of low G (about 3°C/cm) and low R (about 25 ⁇ m/sec) from a melt, poured at 760°C, of the following composition: Si 13.7% Sr 0.30% Ti 0.03% (as TiB2, TiAl3) Cu 2.0% Ni 2.0% Mg 0.66% Fe 0.24% Mn 0.38% Zr 0.04% with each of Zn, Sn, Pb, Cr, Ti (elemental, Na and B (other than as TiB2) being less than 0.02% each, and Ca and P each less than 0.003%, the balance comprising Al apart from incidental impurities.
  • the representation adjacent to the photomicrographs of Figure 10 and designations (a) and (b) thereof have the same relevance as in Figure 2.
  • the photomicrographs of Figure 10 should be compared with those of Figure 2.
  • the structures of Figure 2 exhibits large primary Si particles.
  • the structure of the casting depicted in Figure 10 is not only essentially free from primary Si but also does not feature the Sr intermetallic compound in platelet form. Instead the Sr intermetallic is present as equiaxed, blocky particles.
  • the Ti is necessary to achieve these changes in structure. This effect of Ti on primary Si and Sr intermetallic particles is quite new and unexpected and has not been reported before to the best of our knowledge.
  • Figure 11 further illustrates the significantly enhanced utility resulting from the use of Sr in combination with Ti according to the present invention.
  • the photomicrographs (x20) of Figure 11 illustrate the typical structure in an engine block cast in a zircon sand mould from an alloy according to the invention having 0.30%Sr and 0.04%Ti added as Al-Ti-B, but otherwise the same as the alloy of Figure 3.
  • the alloy depicted in Figure 11 was cast under conditions of low G (about 3°C/cm) and low R (about 10 to 30 ⁇ m/sec) from a melt, poured at 780°C, of the following composition: Si 13.6% Sr 0.30% Ti 0.04%(as TiB2 and TiAl3) Cu 2.0% Ni 2.1% Mg 0.64% Fe 0.22% Mn 0.4% Zr 0.05% with each of Zn, Sn, Pb, Cr, Ti (elemental), Na and B (other than as TiB2) being less than 0.02% each, Ca and P each being less than 0.003% each, and the balance being Al apart from the incidental impurities.
  • the photomicrographs (a) and (b) of Figure 12, respectively x50 and x200, show the structure of a cast 3HA type of alloy having 0.30%Sr and 0.05%Ti added as Al-Ti-B. Again, the structure is characterised by equiaxed, blocky Sr intermetallic particles.
  • the alloy of Figure 12 is further illustrated in the scanning electron micrograph (x150) of Figure 13 taken on a fracture surface of the casting. This micrograph highlights the changed morphology of the Sr intermetallics.
  • Figure 14 illustrates S-N curves for 3HA alloy having less than 0.10% Sr (indicated as “old 3HA") and for a 3HA type alloy having a combination of Sr and Ti in accordance with the present invention (indicated as “modified 3HA").
  • the alloy according to the invention displays substantially higher fatigue strength than the "old 3HA".
  • Ti is added as Al-Ti-B, providing (Al,Ti)B2, TiB2 and TiAl3 to the melt, although essentially the same result is obtained with (Al,Ti)B2, TiB2, or TiAl3 alone or with other forms of Ti detailed herein.
  • Figure 15 shows machinability for similarly designated “old 3HA” and “modified 3HA” in terms of tool life; the "old 3HA” being one with optimum structure as shown in Figure 1.
  • machinability is essentially the same for each alloy, a very similar tool life being achieved with each at any given cutting speed.
  • the machinability of the "modified 3HA” is therefore very much better than for "old 3HA” which comprises areas of typical poor structure containing primary si, as is evident from a comparison of Figures 4 and 15.
  • Sr characterising the present invention is believed to be unique to Sr.
  • Na at a level of about 0.003% in 3HA alloy acts as a modifier and achieves similar modification to the use of about 0.05% Sr in such alloy.
  • increasing the level of Na by approximately 10 times, as typically is done with Sr in the present invention simply results in over modification of the alloys.
  • the photomicrograph (x50) of Figure 16(a) shows the structure of a sand mould cast solid cylinder of a 3HA alloy having 0.003 %Na, but without addition of Sr. This structure is of conventional modified form, and is similar to that obtained with the same alloy having 0.05% Sr without addition of Na - see Figure 1.
  • the photomicrograph (x50) of Figure 16(b) shows the structure of a casting identical to that of Figure 16(a), but using an alloy differing only in that the Na level is increased to 0.05%.
  • Figure 16(b) shows an irregular, over modified structure featuring coarse alpha-aluminium regions between eutectic cells which would lead to rapid crack propagation as reported in patent specification 536976.
  • the degree of primary Si particle flotation was found not to be affected by the level of Na additions. All castings made with alloys having Na at least 10 times the conventional level showed bands of floating primary Si at the top of the castings. Also, unlike castings according to the invention using Sr in combination with Ti, castings using such high levels of Na in combination with Ti did not show any reduction in the concentration of floating primary Si.
  • the key feature of the current invention is the improvement in structure, achieved by the combined effects of Sr and Ti in which Ti is preferably added as at least one of (Al,Ti)B2, TiB2 and TiAl3, and most preferably achieved by the combined effects of Sr and Ti added as TiB2.
  • Ti is preferably added as at least one of (Al,Ti)B2, TiB2 and TiAl3, and most preferably achieved by the combined effects of Sr and Ti added as TiB2.
  • the mechanism by which these elements control the structure is understood to a degree sufficient to indicate the influence of Sr and Ti in a range of Al-(12-15%)Si alloy castings. However, the mechanisms are not sufficiently well understood to enable a full explanation at this stage. What is clear is that adding Sr to modify eutectic Si and/or to widen the coupled zone is known for Sr levels below 0.1%.
  • FIG 17 the window of casting conditions in terms of G and R are depicted, based on the data available. As indicated, the shaded area designates part of those conditions applicable to old 3HA according to patent 536976, while the black area designates the extension of conditions applicable to the alloy of the invention. This shows a lowering of the G and R values for which modified eutectic microstructures are achieved. The expansion of that window is shown to provide a minimum R value of approximately 15 ⁇ m/sec, with the minimum G value reduced to close to zero. While the expanded area is small, it is in the critical area of the window in terms of castability required for alloys cast on a production basis in permanent and sand moulds.
  • the G and R values obtainable with the alloys of the invention cover the solidification conditions existing in sand castings in which the G value typically is less than 5°C/cm and the R value is estimated to be as low as 15 ⁇ m/sec, depending on the section thickness of the cast product.
  • an alloy composition can now be defined which displays all of the characteristics of the alloys defined in patent 536976 but, in addition, now features the improvement that it can be used in a much wider variety of castings without the inevitable need for sophisticated solidification controls.
  • the alloy of the invention is well suited for repetitive casting on a production basis, using permanent and sand moulds. It enables a wide variety of castings to be produced on that basis in such moulds, including castings of complex form and of substantial wall section thickness up to 30 mm and higher.
  • the alloy of the invention is extremely useful in the production of castings in which there is a need for good wear resistance and machinability, high levels of fatigue strength and good ambient and elevated temperature properties such as hardness and tensile strength.
  • These castings include cylinder blocks, cylinder heads (without the need for traditional valve guide and inlet valve seat inserts), transmission and brake components and other engine components such as pistons and rocker arms.
  • Non-automotive or stationary engine applications include door restraint/closure cylinders, moulds for products such as tyres and tiles, pistons and cylinders for compressors, and housings for pumps such as slurry pumps.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Manufacture Of Alloys Or Alloy Compounds (AREA)
  • Continuous Casting (AREA)
  • Powder Metallurgy (AREA)
EP89902718A 1988-02-10 1989-02-10 Cast aluminium alloys Expired - Lifetime EP0400059B1 (en)

Applications Claiming Priority (3)

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AU6681/88 1988-02-10
AUPI668188 1988-02-10
PCT/AU1989/000054 WO1989007662A1 (en) 1988-02-10 1989-02-10 Cast aluminium alloys

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EP0400059A1 EP0400059A1 (en) 1990-12-05
EP0400059A4 EP0400059A4 (en) 1991-07-24
EP0400059B1 true EP0400059B1 (en) 1994-05-25

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JP (1) JP2858838B2 (enrdf_load_stackoverflow)
KR (1) KR970001410B1 (enrdf_load_stackoverflow)
AT (1) ATE106102T1 (enrdf_load_stackoverflow)
AU (1) AU612239B2 (enrdf_load_stackoverflow)
CA (1) CA1329024C (enrdf_load_stackoverflow)
DE (1) DE68915539T2 (enrdf_load_stackoverflow)
ES (1) ES2016004A6 (enrdf_load_stackoverflow)
IN (1) IN173691B (enrdf_load_stackoverflow)
NZ (1) NZ227940A (enrdf_load_stackoverflow)
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CN108929994A (zh) * 2018-07-13 2018-12-04 宜兴市佳信数控科技有限公司 一种大型液压机、成型机专用油缸及其制备方法

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WO1991002100A1 (en) * 1989-08-09 1991-02-21 Comalco Limited CASTING OF MODIFIED Al BASE-Si-Cu-Ni-Mg-Mn-Zr HYPEREUTECTIC ALLOYS
JPH05505343A (ja) * 1989-12-11 1993-08-12 コマルコ　アルミニウム　リミテッド 過共晶Ａ１―Ｓｉ合金の調整鋳造
DE4400896C1 (de) * 1994-01-14 1995-03-30 Bergische Stahlindustrie Bremsscheibe für Scheibenbremsen von Schienenfahrzeugen
US6786983B2 (en) * 2002-03-19 2004-09-07 Spx Corporation Casting process and product
US6923935B1 (en) 2003-05-02 2005-08-02 Brunswick Corporation Hypoeutectic aluminum-silicon alloy having reduced microporosity
US7666353B2 (en) 2003-05-02 2010-02-23 Brunswick Corp Aluminum-silicon alloy having reduced microporosity
KR101664586B1 (ko) * 2014-11-19 2016-10-25 현대자동차주식회사 자동차 엔진 피스톤용 알루미늄 합금 및 그 제조방법
CN110527874A (zh) * 2019-10-16 2019-12-03 南通众福新材料科技有限公司 一种高强度耐磨铝合金材料及制作工艺
CN113862529B (zh) * 2020-06-30 2023-04-07 比亚迪股份有限公司 一种铝合金及其制备方法
DE102023106915A1 (de) 2023-03-20 2024-09-26 Federal-Mogul Nürnberg GmbH Verfahren zur Herstellung einer Bremsscheibe, Bremsscheibe und Verwendung einer Aluminiumlegierung zur Herstellung einer Bremsscheibe

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AU3970368A (en) * 1968-06-25 1969-11-26 Comalco Aluminium Chell Bay) Limited Aluminium base alloys
GB1529305A (en) * 1974-11-15 1978-10-18 Alcan Res & Dev Method of producing metal alloy products
CA1064736A (en) * 1975-06-11 1979-10-23 Robert D. Sturdevant Strontium-bearing master composition for aluminum casting alloys
AU536976B2 (en) * 1980-09-10 1984-05-31 Comalco Limited Aluminium-silicon alloys
US4734130A (en) * 1984-08-10 1988-03-29 Allied Corporation Method of producing rapidly solidified aluminum-transition metal-silicon alloys
JPS6274043A (ja) * 1985-09-27 1987-04-04 Ube Ind Ltd 加圧鋳造用高力アルミニウム合金

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108929994A (zh) * 2018-07-13 2018-12-04 宜兴市佳信数控科技有限公司 一种大型液压机、成型机专用油缸及其制备方法

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IN173691B (enrdf_load_stackoverflow) 1991-06-25
JP2858838B2 (ja) 1999-02-17
DE68915539D1 (de) 1994-06-30
WO1989007662A1 (en) 1989-08-24
DE68915539T2 (de) 1994-09-01
EP0400059A4 (en) 1991-07-24
ATE106102T1 (de) 1994-06-15
NZ227940A (en) 1990-12-21
KR900700642A (ko) 1990-08-16
EP0400059A1 (en) 1990-12-05
CA1329024C (en) 1994-05-03
KR970001410B1 (ko) 1997-02-06
ES2016004A6 (es) 1990-10-01
JPH03503658A (ja) 1991-08-15
AU3069789A (en) 1989-09-06
AU612239B2 (en) 1991-07-04

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