JP2015157588A - aluminum die-cast steering column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum die-cast steering column that further increases base strength by suppressing a deterioration or variations in strength.SOLUTION: An aluminum die-cast steering column for use in a steering lock with an ignition switch for steering for an automobile is made of an aluminum die casting which contains Cu, Si and Mg as essential components by specific amounts, which contains not only Zn, Fe, Mn and Ni but also Ti, Pb, Sn, Cr, Sr, Ca and Na as arbitrary components, and in which the remainder is Al and inevitable impurities. Hardness of its casting surface is set to be HRB 57.5 or more.

Description

  The present invention relates to an aluminum die-cast steering column used for a steering lock with an ignition switch of an automobile steering.

  In order to prevent theft of the automobile, a steering lock device is used that not only stops the engine when the key of the ignition switch is removed but also disables the steering wheel. The steering column, which is the main body of the steering lock device and the mounting portion, must be rigid and cannot be easily broken. It is stipulated that there is no abnormality.

  On the other hand, the structure of the steering is changed from the conventional hydraulic type to the EPS type, the torque applied to the components becomes severe, and the steering column is also required to have high strength. In many cases, a steering column is manufactured by die casting of a light metal such as an aluminum alloy in order to reduce the weight (for example, see Patent Document 1). Various methods are known for the die casting method, but as a method applied to the steering column, after the mold is attached to the die casting machine, the molten aluminum alloy is injected into the mold at high pressure and solidified. The ordinary die casting method for taking out from a mold is widely used. Further, as a countermeasure against the nest, a vacuum die casting method in which the inside of the mold cavity is evacuated and decompressed may be applied.

  However, the ordinary die casting method and the vacuum die casting method have a casting defect, and therefore, if an excessive torque is applied, the die may be broken, and how to secure the strength is important. These casting defects include various defects such as cast holes, fractured chill layers, and coarse α-phase, and it is difficult to obtain products that do not have strength variation by controlling these defects completely by the ordinary die casting method or vacuum die casting method. Met. In addition, the conventional aluminum alloy for JIS standard casting does not have a remarkable improvement in product strength even if a special die casting method such as a vacuum die casting method is used. It was limited.

JP 2008-265358 A

  The present invention has been made in view of such a situation, and an object of the present invention is to provide an aluminum die-cast steering column in which strength reduction and variation are suppressed and base strength is further improved.

In order to solve the above problems, the present invention provides the following aluminum die-cast steering column.
(1) In an aluminum die-cast steering column used for a steering lock with an ignition switch of an automobile steering,
The material composition is, by mass%, Cu: 5.0% or less, Si: 6.5 to 12.0%, Mg: 0.1 to 0.6% as essential components, and Zn: 1.0 as an optional component. % Or less, Fe: 1.3% or less, Mn: 0.6% or less, Ni: 0.05% or less, Ti: 0.5% or less, Pb: 0.2% or less, Sn: 0.2% or less , Cr: 0.05% or less, Sr: 0.2% or less, Ca: 0.2% or less, Na: 0.2% or less, the balance being Al and inevitable impurities, and the casting surface An aluminum die-cast steering column characterized by having a hardness of HRB57.5 or higher.
(2) The aluminum die-cast steering column as described in (1) above, wherein the tensile strength σB is 280 MPa or more and the elongation is 4.0% or more.

  According to the present invention, by using an aluminum alloy for casting containing Cu, Si, Mg as essential components and further containing Ti, Sr, Ca, Na, etc. as optional components, strength reduction and variation can be suppressed. A steering column made of aluminum die-casting with improved strength is provided.

It is a perspective view which shows an example of a steering column. It is a side view which shows the shape of a test piece, and the dimension of each part.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an example of a steering column. The steering column 1 is a hollow cylinder, and has a key hole 2 formed therein. A steering shaft (not shown) is inserted inside, and a key is inserted into the key hole 2 of the steering column 1 to lock the steering shaft.

  In the present invention, the steering column 1 is made of an aluminum die casting containing Cu, Si and Mg as essential components. Although these essential components will be described below, each content is mass% with respect to the total amount of the aluminum alloy.

Cu is an element effective for increasing the mechanical strength. However, if the content exceeds 5.0%, a large amount of intermetallic compounds such as CuAl ₂ are crystallized or precipitated at the grain boundaries, and breakage occurs. Reduce elongation. Therefore, the Cu content is 5% or less. In addition, although there is no restriction | limiting in a minimum, in order to ensure the improvement of mechanical strength, 0.1% or more is required. A preferable Cu content is 3.5 to 5.0%.

  Si is added to increase the mechanical strength as well as Cu, and to increase the hardness and fluidity. In order to ensure mechanical strength, hardness, and fluidity, the content needs to be 6.5% or more. However, if it exceeds 12.0%, the elongation decreases, so the content is made 12.0% or less. A preferable Si content is 6.5 to 8.0%.

  Mg is an element effective for increasing the tensile strength and hardness, but such an effect cannot be exhibited when the content is less than 0.1%. However, when the content exceeds 0.6%, the toughness is lowered. A preferable Mg content is 0.4 to 0.6%.

  In addition, in any case, in order to further improve the surface hardness, tensile strength, elongation and the like to improve the quality, Zn is 1.0% or less (preferably 0.3% or less) and Fe is 1. 3% or less (preferably 0.5% or less), Mn 0.6% or less (preferably 0.5% or less), Ni 0.05% or less (preferably 0.04% or less), Ti 0 0.5% or less (preferably 0.2 to 0.5%), Pb 0.2% or less (preferably 0.05% or less), Sn 0.2% or less (preferably 0.05% or less) ), Cr is 0.05% or less (preferably 0.04% or less), Sr is 0.2% or less (preferably Sr: 0.02 to 0.2%), and Ca is 0.2% or less ( Preferably, Ca: 0.02 to 0.2%) and 0.2% or less (preferably 0.02 to 0.2%) of Na can be added. In addition, the minimum of content of these elements is 0%.

  These optional elements are added depending on the purpose. For example, by adding Sr, the plate-like Si can be spheroidized to improve toughness and elongation. Moreover, crystal grain refinement progresses by addition of Ti, and spheroidization of plate-like Si progresses by addition of Ca or Na. These optional components may be added alone or in admixture of two or more.

  In addition, as an aluminum alloy of the above alloy composition, AC4C and AC4CH, which are Al—Si—Mg based aluminum alloys of JIS H5202, ADC10 and ADC12 which are Al—Si—Cu based aluminum alloys of JIS H5302, or Cu and Mg Furthermore, a material added with a predetermined amount of an optional component can also be used.

  By die casting the above aluminum alloy, for example, it is cast into a steering column having the shape shown in FIG. As the die casting method, a semi-solid die casting method (hereinafter, “sleeve method”) of a sleeve method is used.

  In this sleeve method, a device in which a sleeve is connected to a cavity of a general die casting machine is used, and when the mold clamping is completed, the molten aluminum alloy is injected from a pouring port of the sleeve, and injection is performed by a plunger. Then, the mold is opened, and the cast product (steering column) is taken out from the mold.

  In the sleeve method, it is possible to obtain a compact having a fine particle size compared to other die casting methods. For this purpose, it is necessary to achieve a larger degree of supercooling (large cooling rate) and to generate more nuclei. Therefore, it is necessary to optimize the pouring temperature, the sleeve size, the sleeve temperature, the sleeve filling rate and the cooling rate, and the effect of the sleeve filling rate is great. The sleeve filling rate is a ratio (A / S × 100 (%)) between a cross-sectional area (S) in a cross section perpendicular to the longitudinal direction of the sleeve and a cross-sectional area (A) of the pouring after pouring. . As the sleeve filling rate decreases, the contact area between the molten metal and the sleeve increases. Therefore, by reducing the sleeve filling rate and increasing the shot time lag (time from pouring to the sleeve until injection), the cooling rate in the sleeve can be increased and nucleation can be promoted.

  For the sleeve method, International Publication No. 2013/039247 can be referred to.

  In such a sleeve method, the casting surface of the steering column 1 obtained by reducing the sleeve filling rate, increasing the shot time lag, and adjusting the pouring temperature, sleeve size, sleeve temperature, etc. The hardness of the surface can be HRB 57.5 or more. If the hardness is less than HRB57.5, sufficient mechanical strength, durability and dimensional stability cannot be obtained. Preferably, it is set to HRB62.0 or more.

  Further, in order to further improve the quality of the steering column 1, the tensile strength σB is 280 MPa or more, preferably 315 MPa or more, and the elongation is 4.0% or more, preferably 7.0% or more.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is further demonstrated, this invention is not restrict | limited at all by this.

(Examples 1-16, Comparative Examples 1-16)
JIS H5202 Al-Si-Mg-based aluminum alloy AC4C or AC4CH, JIS H5302 Al-Si-Cu-based aluminum alloy ADC10 or ADC12, or optional components such as Cu, Mg, and Sr and Ti Were added in predetermined amounts to prepare aluminum alloys of Examples and Comparative Examples shown in Table 1.

And in Example and Comparative Examples 2-4, Comparative Examples 6-8, Comparative Examples 10-12, and Comparative Examples 14-16 using an aluminum alloy, the casting conditions are changed as shown in FIG. The steering column shown was die cast. In Comparative Examples 1, 5, 8, and 13, steering columns having the same shape were obtained by the ordinary die casting method. Then, test pieces having the shapes and dimensions shown in FIG. 2 were cut out from the periphery of the steering column key lock, tested under the following conditions, and the Rockwell hardness HRB of the test piece grip after the test was measured. The measurement surface at this time was a casting surface. The results are shown in Table 1.
(Test conditions)
Testing machine: Instron tensile and compression testing machine Tensile speed: 0.5 mm / min
Test piece elongation measurement by video extensometer

  As shown in the examples, all of the test pieces cast by the sleeve method with the alloy composition according to the present invention have a hardness of the cast skin surface of HRB 57.5 or more, and further a tensile strength of 280 MPa or more and an elongation of 4 0.0% or more.

  Further, from the comparison between Examples 1, 5, 9, and 13 and Comparative Examples 1, 5, 9, and 13, even if the same material was used, casting was performed by a normal die casting method by casting by a sleeve method. It can be seen that the hardness, tensile strength, and elongation become superior compared to the case.

  When Cu and Sr are added as in Examples 2, 6, 10, and 14, the hardness, tensile strength, and elongation are superior to those of Examples 1, 5, 9, and 13. This is because the toughness / elongation is improved by the improvement of hardness and base strength by addition of Cu and the spheroidization of plate-like Si by addition of Sr.

  By adding Mg to the materials of Examples 2, 6, 10, and 14 as in Examples 3, 7, 11, and 15, the hardness, strength, and elongation are further improved. This is because the addition of Mg improves the strength while inhibiting the improvement of the elongation, but the elongation is improved by the addition of Sr, so the concern due to the addition of Mg is eliminated.

  By adding Ti, Ca, and Na to the materials of Examples 3, 7, 11, and 15 as in Examples 4, 8, 12, and 16, the amount of improvement in hardness, tensile strength, and elongation becomes the largest. . This is because crystal grain refinement by adding Ti and spheroidization of plate-like Si by adding Ca or Na progress.

  On the other hand, in Comparative Examples 2 to 4, 6 to 8, 10 to 12, and 14 to 16, the material component is outside the scope of the present invention, and the improvement in hardness, tensile strength, and elongation is achieved even when the sleeve method is applied. Few.

1 Steering column 2 Key hole 2

Claims (2)

In the aluminum die-cast steering column used for steering lock with ignition switch for automobile steering,
The material composition is, by mass%, Cu: 5.0% or less, Si: 6.5 to 12.0%, Mg: 0.1 to 0.6% as essential components, and Zn: 1.0 as an optional component. % Or less, Fe: 1.3% or less, Mn: 0.6% or less, Ni: 0.05% or less, Ti: 0.5% or less, Pb: 0.2% or less, Sn: 0.2% or less , Cr: 0.05% or less, Sr: 0.2% or less, Ca: 0.2% or less, Na: 0.2% or less, the balance being Al and inevitable impurities, and the casting surface An aluminum die-cast steering column characterized by having a hardness of HRB57.5 or higher.   2. The aluminum die-cast steering column according to claim 1, wherein the tensile strength [sigma] B is 280 MPa or more and the elongation is 4.0% or more.

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