Classifications

• • 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. We previously have proposed an Al-(ll-20%)Si alloy
• the Jenkinson alloy (herein referred to as the Jenkinson alloy) , which 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:
• SU B STITUTESHEET R of the solid phase is 10 to 5000 microns/sec and the temperature gradient G at the solid/liquid interface is from
• Such solidification conditions are controlled to produce the Jenkinson alloy with a micro- structure 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 microns in diameter, and preferably less than 1 micron diameter.
• the hypereutectic Jenkinson alloy 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.
• 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: Canadian 1175867 Swedish 454446 French 2489846 United States 4434014
• the 3HA alloy is much improved, compared with the
• 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
• SUBSTITUTE SHEET 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. While such formation of primary Si is detrimental in itself, it also depletes the matrix of Si, resulting in the matrix featuring large areas of alpha-aluminium in dendrite form together with Al-Si eutectic. The detrimental effects of primary Si and related features in the 3HA alloy results in a large reduction in machinability, fatigue strength and wear resistance.
• 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 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.
• SUBSTITUTE SHEET achieves very beneficial effects. Specifically, we have found that when Sr is added to the alloys of the invention in excess of 0.10%, it does not widen the coupled zone sufficiently to eliminate the presence of primary Si particles in complex castings but instead it substantially prevents those primary Si particles that do form from floating. This is an unexpected result.
• 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%. While Sr intermetallic particles still are formed, 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
• 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)Bition, TiBvalent and
• TiAl_ can achieve the same effects as the above compounds.
• other similar compounds such as TiC and TiN can achieve the same effects as the above compounds.
• 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.
• Al-Si alloy having 12-15% Si comprising:
• melt of the alloy with Sr present at a level in excess of 0.10% together with Ti present, as described above, at a level in excess of 0.005%, the melt further comprising:
• 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 contains Sr in excess of 0.10% together with Ti in excess of 0.005%, the alloy further comprising:
• the alloy has a microstructure in which any primary Si present is substantially uniformly dispersed and is substantially free of segregation, and in which substantially uniformly dispersed Sr intermetallic particles are present but are substantially free of such particles in the form of platelets, the microstructure predominantly comprising a eutectic matrix.
• 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 levels of Sr in excess of 0.10% in conjunction with Ti in excess of 0.005%.
• the resulting satisfactory microstructure is therefore achieved through chemical means, whereas previously the same results have been sought to be achieved by closely controlled solidification techniques, including close controls on metal and die temperatures. In such case, the precise closely controlled solidification techniques, as previously have been attempted, have also been dictated by the increasing
• a level of Sr only slightly in excess of 0.10% generally is suitable only for relatively simple or thin wall section castings produced in a permanent mould.
• 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 format on of pr mary S and thus s mply ncrease the tendency for the formation, and difficulty in control, of
• Sr intermetallics Depending on the complexity of the casting or its wall section thickness as referred to earlier, a typical 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 preferably 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 TiAl_ as in Al-Ti master alloy, the Ti level preferably should not exceed 0.25%.
• the level of Ti required is dictated in part by, and generally increases with, the level of Sr in excess of 0.10%.
• 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.
• Sr at a level in excess of 0.10%, 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
• SUBSTITUTE SHEET substantially fully eutectic microstructures.
• the alloys of the invention if required, also can include Na, a known modifier for this latter purpose.
• such know modifier if present, is used within its normal range of up to 0.01%, and is additional to the use of Sr at a level in excess of 0.10%. Excess levels of Na by itself will not have th desired effect.
• the alloy and method of casting have been defined in terms of its Si, Sr and Ti content, as well as other alloyin additions present.
• the additions of Cu, Ni, Mg, Fe, Mn and Z are to provide strengthening and hardening intermetalli compounds.
• the mel and alloy of the invention can include Zn, Sn, Pb and Cr. These elements, in general, do not confer a significan befneficial effect but also do not have adverse consequence where used below the respective limits specified above; although, if present, they should not exceed those limits t avoid adverse consequences.
• the process disclosed therein for the production of alloy 3HA entails the use of specific cooling conditions, comprising solidification of a melt of the alloy such that:
• the growth rate R of the solid phase during solidification is from 150 to 1000 microns per second;
• the temperature gradient G at the solid/liquid interface, expressed in C/cm, is such that the ratio G/R is from 500 to 8000°Cs/cm 2 .
• 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
• Ti is found not t achieve an additional benefit in changing intermetalli morphology but has a tendency to increase primary Si formation.
• the composition of the alloy requires the carefu selection of these alloying elements and the correc proportions of each to achieve optimum benefit. In most case 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.
• Zr provide intermetallic compounds which form part of the eutectic microstructure and are based principally on the
• the eutectic intermetallic particles are principally silicon but Cu-Ni-Al, Cu-Fe-Ni-Al and other complex intermetallic phases also may be present. Naturally, as particle size increases so does the propensity for cracking under applied loads. For this reason the intermetallic particles comprising the eutectic must be fine (less than 10 microns in diameter), preferably uniformly dispersed and preferably with an inter-particle spacing not greater than 5 microns.
• 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
• SUBSTITU 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:
• 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 microns in diameter, preferably equiaxed, preferably uniformly dispersed and preferably with an interparticle spacing not greater than 5 microns.
• 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.
• SUB ST IT 800°C/cm and the growth rate, R be in the range of 150 microns/sec to 1000 microns/sec giving a G/R range of 500 to
• 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 microns/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 microns/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.
• 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 in excess of 0.10% in a melt ' to form an ingot of the alloy of the invention, or just prior to casting 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% 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 present invention exhibit significantly enhanced fatigue strength compared with th alloy of patent 536976. Also, while tensile strength can b slightly, but not significantly, reduced compared with th alloy of patent 536976, other physical properties such a hardness and resistance to wear are essentially the same a for the alloy of that patent. Thus, overall, 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(a) and (b) are photomicrographs showing the optimum microstructures for 3HA alloy according to patent
• Figures 2(a) and (b) and Figures 3(a) and (b) are photomicrographs showing typical poor microstructures for 3HA alloy according to patent 536976;
• Figure 4 is a graph illustrating the detrimental influence of primary Si on the machinability of 3HA alloy according to patent 536976;
• Figure 5 is a bar chart representation illustrating the influence of primary Si on the fatigue strength of 3HA
• Figure 6(a) and (b) are photomicrographs of a casting produced from alloy 3HA according to patent 536976;
• Figures 7(a) and (b) are photomicrographs of a casting according to the present invention.
• Figure 8 is a scanning electron photomicrograph and x-ray analysis of the surface of a fractured casting according to the present invention.
• Figure 9 is a graph of tensile strength versus Sr content in 3HA base alloy, with one point (average of multiple tests) for an alloy according to the present invention.
• Figures 10(a) and (b) are photomicrographs showing microstructures of castings according to the present invention.
• Figures 11(a) and (b) are further photomicrographs showing microstructures of castings according to the present invention.
• Figures 12(a) and (b) are further photomicrographs of an alloy according to the present invention.
• Figure 14 is a graph showing respective S-N curves for 3HA alloy according to patent 536976 and the present invention.
• Figure 15 is a graph showing respective machinability curves for 3HA alloy according to patent 536976 and the present invention.
• Figures 16(a) and (b) are respective photomicrographs showing microstructures of 3HA alloy having Na as modifier respectively at conventional levels and at a higher level;
• Figure 17 is a diagram showing part of the relationship between G and R for 3HA according to specification 536976 and, with the addition of Sr and Ti, according to the present invention.
• Figures 1 to 3 in their respective photomicrographs
• 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 these 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
• 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.
• EET outer extremity of the fins due to the relatively rapid cooling obtained.
• the microstructure progressively deteriorated at higher levels of the main wall and at radially inner regions of the fins.
• 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
• T TESHEET (b) of Figure 6 respectively xl3 and x60, for a 3HA allo according to patent 536976 containing 0.05% Sr. As shown i
• Figure 6 primary Si has floated during solidification, an concentrated beneath a "ledge" in the casting.
• the present invention provides a chemical method fo widening the range of necessary solidification conditions an controlling microstructure, thereby eliminating the need fo such stringent control over solidification conditions.
• Sr at a level in -excess of 0.1% with Ti in exces of 0.005% is used in a novel manner to ensure formation o substantially fully eutectic microstructures.
• the addition of high level of Sr has been found to hav beneficial effects on the structure of Al-(12-15%) Si alloys.
• Sr has the effec of preventing the flotation and reducing the number, but no eliminating, primary Si particles formed durin solidification; this resulting in a uniform dispersion o relatively coarse Si particles throughout the casting.
• Thi is illustrated in the photomicrograph (x50) of Figure 7(a), for a 3HA type of alloy containing 0.3% Sr, and no T additions.
• 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
• the tensile strength curve of Figure 9 is drawn through asterisk points for alloy substantially free of Ti.
• FIG. 9 also shown in Figure 9 is 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-l% 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
• FIG. 10 The photomicrographs (x20) of Figure 10 illustrate typical improved structures obtained in a complex finned cylinder cast in a zircon sand mould from.an alloy according to the present invention with 0.3%Sr and 0.03%Ti added as Al-Ti-B.
• the component depicted in Figure 10 was cast under conditions of low G (about 3°C/cm) and low R (about 25 microns/sec) from a melt, poured at 760°C, of the following composition:
• 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.
• Figure 11 further illustrates the significantly enhanced utility resulting from the use of Sr in combination with Ti according to the present invention.
• SUBSTITUTESHEET 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 microns/sec) from a melt, poured at 780 C, of the following composition:
• Figure 11 and the designations (a) to (c) thereof have the same relevance as in Figure 3.
• the structures in Figure 3 exhibit large, primary Si particles, while those of Figure 11 are substantially free of such particles and have Sr intermetallic particles present as equiaxed, blocky particles.
• Figure 15 shows machinability for similarly designated
• 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)B 2 , TiB 2 and TiAl 3 , and most preferably achieved by the combined effects of Sr and Ti added as TiB,,.
• Ti is preferably added as at least one of (Al,Ti)B 2 , TiB 2 and TiAl 3 , and most preferably achieved by the combined effects of Sr and Ti added as TiB,,.
• 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
• SUBSTITUTE SHEET that adding Sr to modify eutectic Si and/or to widen the coupled zone is known for Sr levels below 0.1%. What was not known prior to the present invention, and could not have been predicted, was that levels of Sr in excess of 0.1%, such as from 0.11%, did not widen the coupled zone enough, to eliminate the primary Si, but instead stopped flotation of such primary Si particles as are able to form. Moreover, while Ti as., TiB shortcut or TiAl_ is known to nucleate primary aluminium, it was totally unexpected that it would further reduce the amount of primary Si present and change the morphology of Sr intermetallic particles from platelets to substantially equi-axed blocky particles. In the latter regard, it may have been predicted that the addition of Ti would simply nucleate finer platelike Sr particles but this is not the case.
• 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 microns/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. That is, the G and R values solidification conditions existing in sand castings in whic the G value typically is less than 5 C/cm and the R value i estimated to be as low as 15 microns/sec, depending on th section thickness of the cast product.
• an alloy composition can now b defined which displays all of the characteristics of th alloys defined in patent 536976 but, in addition, now feature the improvement that it can be used in a much wider variety o castings without the inevitable need for sophisticate solidification controls.
• the alloy of the invention is well suited fo repetitive casting on a production basis, using permanent an sand moulds. It enables a wide variety of castings to b produced on that basis in such moulds, including castings o complex form and of substantial wall section thickness up to
• the alloy of the invention is extremel useful in the production of castings in which there is a nee 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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• 1989
  • 1989-02-10 AU AU30697/89A patent/AU612239B2/en not_active Ceased
  • 1989-02-10 ES ES8900806A patent/ES2016004A6/es not_active Expired - Lifetime
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  • 1989-02-10 WO PCT/AU1989/000054 patent/WO1989007662A1/en active IP Right Grant
  • 1989-02-10 DE DE68915539T patent/DE68915539T2/de not_active Expired - Fee Related
  • 1989-02-10 AT AT89902718T patent/ATE106102T1/de not_active IP Right Cessation
  • 1989-02-10 EP EP89902718A patent/EP0400059B1/en not_active Expired - Lifetime
  • 1989-02-10 NZ NZ227940A patent/NZ227940A/en unknown
  • 1989-02-10 CA CA000590803A patent/CA1329024C/en not_active Expired - Fee Related

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