Aluminum alloy die-casting plunger head material matched with thermal expansion coefficient of h13 cylinder and preparation method thereof

Abstract

The application discloses an aluminum alloy pressure casting plunger head material matched with the thermal expansion coefficient of H13 cylinder and a preparation method thereof, and belongs to the technical field of metal materials and aluminum alloy pressure casting. The chemical composition of the material is as follows in terms of percentage by weight: C 3.70-3.75%, Si 1.80-2.20%, Mn 0.60-0.70%, P ≤0.04%, S ≤0.02%, Cr 0.30-0.40%, Cu 0.70-0.80%, Mo 0.25-0.30%, Sb 0.005-0.007%, and the balance is Fe. The application precisely controls the thermal expansion behavior of the material at 25-700 DEG C through the synergistic effect of Cu and Mo, so that the deviation of the expansion coefficient of the material from that of the H13 cylinder is less than or equal to 5%, and the expansion difference stress in the heating stage is eliminated from the root. Meanwhile, high pearlite structure is obtained by combining low Cr and trace Sb, and the high-temperature oxidation resistance and non-stick aluminum characteristics are improved by using appropriate Si.

Description

Technical Field

[0001] This invention relates to the field of metal materials and aluminum alloy die casting technology, specifically to a plunger head material for an aluminum alloy die casting machine and its preparation method. Background Technology

[0002] The plunger head (also known as the injection head) is a core consumable of aluminum alloy die casting machines. It works in conjunction with the expensive H13 mold steel cylinder and reciprocates under harsh working conditions of high temperature (about 700°C), high pressure, and high-speed erosion.

[0003] Traditional plunger head materials (such as ordinary ductile iron, alloy cast iron with only Sb added, or high-Cr wear-resistant cast iron) are designed primarily with a focus on room temperature hardness and wear resistance, neglecting the thermophysical properties during the heating phase from room temperature to the operating temperature of 700°C. Through long-term field observation and data analysis, the inventors of this invention discovered that over 60% of the wear, scoring, and even seizing of the plunger head and barrel occur during the heating phase of equipment startup, rather than the normal die-casting phase when the temperature is stable.

[0004] The fundamental reason lies in the mismatch in thermal expansion coefficients between the traditional materials and the H13 barrel. During the heating process: If the plunger head expands too much, it will squeeze, scratch, or even "seize" the expensive H13 barrel. If the expansion of the plunger head is too small, it will result in an excessively large clearance, leading to "cold loosening," impact wear, and material leakage.

[0005] Currently, existing technologies and publicly available patents mainly focus on increasing hardness by adding alloys or improving lubrication through structural design, but none of them address the protection of the H13 barrel during the heating phase from the perspective of synergistic design of thermal expansion coefficients. Therefore, developing a plunger head material that expands synchronously with the H13 barrel during the heating phase, does not loosen when cold, and does not seize when hot has significant industrial value. Summary of the Invention

[0006] The purpose of this invention This invention provides an aluminum alloy die-cast plunger material and its preparation method that match the thermal expansion coefficient of H13 barrels. This solves the problems of traditional plunger heads causing significant damage to H13 barrels and rapid wear during the heating stage, achieving a synergistic effect of "no loosening in cold state, no seizing in hot state, no tearing, and no seizing", and significantly extending the service life of high-value H13 barrels.

[0007] Technical solution An aluminum alloy die-cast plunger material with a coefficient of thermal expansion matching that of an H13 barrel, characterized in that the chemical composition of the material, by weight percentage, is: C: 3.70%~3.75% Si: 1.80%~2.20% Mn: 0.60%~0.70% P: ≤0.04% S: ≤0.02% Cr: 0.30%~0.40% Cu: 0.70%~0.80% Mo: 0.25%~0.30% Sb: 0.005%~0.007% The balance consists of Fe and unavoidable impurities; The carbon equivalent (CE) is controlled between 4.31 and 4.50, and the material microstructure is slightly hypereutectic to avoid graphite floating and looseness.

[0008] The material has an average coefficient of linear expansion of 11.2 × 10⁻⁶ in the temperature range of 25℃ to 700℃. -6 / K~13.2×10 -6 The coefficient of thermal expansion of / K and H13 mold steel in this temperature range differs by ≤5%.

[0009] Preferred solution The material has a cast pearlite content of ≥90%, and a pearlite content of ≥95% after normalizing treatment, and is free of free cementite and phosphine eutectic.

[0010] After laser surface hardening, the surface hardness of the material reaches 52-58 HRC, while the matrix retains its original toughness. The laser surface hardening process parameters are: laser power 2.5-3.5 kW, scanning speed 200-400 mm / min, and spot diameter 3-5 mm.

[0011] The preparation method of the material includes smelting, furnace inoculation, casting, normalizing treatment and laser surface quenching steps; the furnace inoculation uses a barium silicon inoculant with an addition amount of 0.3% to 0.4% and a casting temperature of 1360 to 1380°C.

[0012] Beneficial effects 1. High thermal expansion matching, protecting H13 barrel: The linear expansion coefficient of the material of this invention deviates from that of H13 mold steel by ≤5% at 25℃-700℃, which greatly reduces the expansion difference stress during the heating stage, eliminates the risk of scratching and seizing of high-value H13 barrel from the source, and extends the barrel life.

[0013] 2. Significantly improved service life: Through extensive installation and comparative testing, the average service life of the plunger head of this invention is 5.5 times that of ordinary ductile iron, 3 times that of alloy ductile iron with only Sb added, and 1 time that of similar products with unbalanced alloy composition (such as high Cr or improper Cu / Mo ratio). Its performance reaches more than 95% of that of pure H13 plunger heads.

[0014] 3. Reduced overall cost: While achieving performance similar to H13, the material cost is much lower than that of the overall H13 plunger head, and the overall operation and maintenance cost of the die-casting unit is significantly reduced due to the protection of the barrel.

[0015] 4. Good process stability: Through precise composition control and inoculation treatment, the material has a uniform structure and good consistency in casting properties, making it suitable for mass production.

[0016] 5. Adapted to laser surface hardening process, achieving surface hardness and internal toughness: The alloy ratio of the material in this invention (especially the synergistic effect of Cu, Mo, and Cr) enables it to obtain a uniform and dense hardened layer (hardness ≥ 52 HRC) during laser surface hardening, while the matrix maintains the good toughness of a high pearlitic structure. This "surface hardness and internal toughness" characteristic ensures the wear resistance of the plunger head surface and avoids the high cost or brittleness risks that may result from integral hardening (such as H13 integral vacuum hardening).

[0017] 6. Superior "soft-hardness matching" with H13 barrel: After laser surface hardening, the surface hardness (52-58 HRC) of the plunger head of this invention is slightly lower than the overall vacuum hardening hardness (55-60 HRC) of H13. However, this "microscopic hardness difference" combined with "macroscopic expansion synchronization" forms a better wear matching in the friction pair - it will not damage the barrel due to excessive hardness, and it can also ensure its own long service life. Attached Figure Description

[0018] Figure 1 Comparison of the thermal expansion curves of the material of the present invention (Example 1) and H13 mold steel at 25℃-700℃.

[0019] Figure 2 Metallographic image of the material of this invention (100×, high pearlite matrix + spheroidization grade).

[0020] Figure 3 : A bar chart comparing the installation life of the plunger head of this invention with that of a comparative plunger head. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] An aluminum alloy die-cast plunger material with a thermal expansion coefficient matching that of an H13 barrel is described. The chemical composition of this material, by weight percentage, is: C 3.70%–3.75%, Si 1.80%–2.20%, Mn 0.60%–0.70%, P ≤0.04%, S ≤0.02%, Cr 0.30%–0.40%, Cu 0.70%–0.80%, Mo 0.25%–0.30%, Sb 0.005%–0.007%, with the balance being Fe and unavoidable impurities. The average linear expansion coefficient of this material in the temperature range of 25℃–700℃ is 11.2 × 10⁻⁶. -6 / K~13.2×10 -6 / K, and the coefficient of thermal expansion of H13 mold steel in this temperature range deviates by ≤5%.

[0023] The carbon equivalent (CE) of the material is controlled between 4.31 and 4.50.

[0024] The material has a cast pearlite content of ≥90%, and a pearlite content of ≥95% after normalizing treatment, with no free cementite or phosphorus eutectic. After laser surface hardening treatment, the surface hardness of the material reaches 52-58 HRC.

[0025] The method for preparing aluminum alloy die-cast plunger head material includes the following steps: Smelting: The chemical composition of raw materials is prepared and then smelted to obtain molten iron; Inoculation treatment: Inoculation treatment is carried out at the time of tapping. The inoculant is barium silicon or an equivalent inoculant, and the amount added is 0.4% to 0.6% of the weight of molten iron. Casting: Control the casting temperature to 1340~1390℃ to obtain the plunger head blank; Normalizing treatment: The blank is normalized; the normalizing treatment process is as follows: heating to 880℃~920℃, holding at that temperature for 1.5~2.5 hours, and then air cooling. Laser surface hardening: The working surface of the plunger head after normalizing is subjected to laser surface hardening. The laser power is 2.5–3.5 kW, the scanning speed is 200–400 mm / min, and the spot diameter is 3–5 mm. After laser surface hardening, the depth of the hardened layer is 1.0–1.5 mm, and the uniformity of the hardness of the hardened layer is controlled within ±2 HRC.

[0026] An aluminum alloy die-casting machine plunger head is made of the material described in any one of claims 1-4, or prepared by the method described in any one of claims 5-7.

[0027] The core principle and synergistic mechanism of this invention This invention is not a simple superposition of alloying elements, but rather achieves functional mutual support and synergy through a specific ratio, jointly achieving the technical effects of "expansion matching" and "protection of the barrel": 1. Synergistic expansion regulation of Cu and Mo: Cu lowers the austenite transformation temperature (by approximately 30-50°C), delaying the expansion behavior of the matrix in the early stages of heating; Mo forms dispersed Mo2C carbides, which pin grain boundaries at high temperatures (>500°C), inhibiting matrix softening and stabilizing the microstructure. The synergistic effect of these two materials results in an instantaneous thermal expansion curve that closely matches the H13 barrel temperature across the entire heating range of 25°C-700°C (see attached figure). Figure 1 (as shown in Table 1), which eliminates the "locking" stress and "tear" behavior caused by the difference in expansion at its source.

[0028] 2. Synergistic effect of low Cr and trace Sb on tissue stability: By controlling the Cr content at 0.3%-0.4% (significantly lower than the 0.5%-1.0% of conventional wear-resistant cast iron), the formation of coarse, brittle Cr7C3 type carbides due to high Cr content is avoided. These hard particles, after peeling off during friction, become abrasive grains, severely damaging the inner wall of the H13 barrel. Simultaneously, Sb exists in trace amounts of 0.005%-0.007%, uniformly distributed at the grain boundaries, promoting pearlite refinement (gradient size increased from the conventional level 5 to level 7 or higher) and inhibiting ferrite formation without causing Sb segregation brittleness. These two factors synergistically achieve the ideal wear-resistant microstructure of "high pearlite (≥95%) + no hard particles".

[0029] 3. Si's interfacial barrier and antioxidant effects: When the Si content is in the range of 1.8%-2.2%, a dense Fe2SiO4 oxide layer can be formed on the material surface under high-temperature working conditions (approximately 700℃). This oxide layer resists the wetting and adhesion of the molten aluminum alloy ("non-stick aluminum"), and forms an "oxide film-oxide film" friction pair with the oxide film on the surface of the H13 barrel, avoiding direct contact between the metal substrate and significantly reducing the coefficient of friction and wear rate.

[0030] Example 1 (Invention) The raw materials were prepared according to the following weight percentages: C 3.72%, Si 2.0%, Mn 0.65%, P 0.03%, S 0.015%, Cr 0.35%, Cu 0.75%, Mo 0.28%, Sb 0.006%, with the balance being Fe. Melting was carried out in a medium-frequency induction furnace. After adjusting the composition before the furnace, the tapping temperature was controlled at 1500±10℃. Inoculation treatment was performed using the ladle-filling method, with the addition of 0.35% barium silicon inoculant (Si: 70%, Ba: 4%). The pouring temperature was 1370℃, and the casting was formed into plunger head blanks. After cleaning, the castings underwent normalizing treatment: heated to 900℃ and held for 2 hours, followed by air cooling. After normalizing, the working surface of the plunger head is subjected to laser surface hardening treatment. The process parameters are: laser power 3.0 kW, scanning speed 300 mm / min, spot diameter 4 mm, hardened layer depth 1.2-1.5 mm, and surface hardness 55 HRC.

[0031] Comparative Example 1 (Standard Ductile Iron) Commercially available ordinary ductile iron plunger heads, without added alloying elements such as Cu, Mo, and Sb. They also undergo laser surface hardening treatment (parameters same as in Example 1).

[0032] Comparative Example 2 (with only Sb added) The chemical composition is similar to that of Example 1, but Cu and Mo are not added, only Sb 0.01% is added. Laser surface hardening treatment is also performed (parameters are the same as in Example 1).

[0033] Comparative Example 3 (Imbalance in Alloy Addition) Cu, Mo, Cr, and Sb were added, but the Cr content was too high (0.6%), and the Cu / Mo ratio was inappropriate (Cu 0.5%, Mo 0.4%). Laser surface hardening was also performed (parameters same as in Example 1).

[0034] Comparison Example 4 (High-end ductile irons from leading domestic companies) A high-end alloy ductile iron plunger head from a well-known domestic brand was purchased. It underwent laser surface hardening treatment (parameters same as in Example 1).

[0035] Comparative Example 5 (pure H13) The plunger head, machined from commercially available H13 mold steel, undergoes integral vacuum quenching and tempering treatment, achieving a hardness of 52-55 HRC (uniform throughout).

[0036] Performance testing 1. Chemical composition and metallographic structure

[0037] 2. Thermal expansion performance test According to the method of GB / T 4339-2008, the coefficient of linear expansion (α) of each sample and H13 die steel at 25℃-700℃ was tested. The results are shown in the table below. Figure 1 .

[0038]

[0039] As can be seen from the data in the table, the expansion coefficient deviation between the material of Example 1 of the present invention and H13 is ≤2.6% throughout the entire heating range, which is much lower than that of the comparative example.

[0040] 3. Hardness and service life test

[0041] Note: • The service life benchmark is the average service life of Comparative Example 1 (ordinary ductile iron); • All cast iron samples (Example 1, Comparative Examples 1-4) underwent the same laser surface hardening process; • The pure H13 sample (Comparative Example 5) was subjected to overall vacuum quenching, and its hardness was uniform throughout. The test was conducted on a 400T die-casting machine, using die-cast aluminum alloy ADC12. The wear of the plunger head diameter and the condition of the inner wall of the barrel were recorded every 2 hours.

[0042] 4. Wear percentage analysis during the heating phase The wear of the friction pair between the present invention and the H13 barrel was tested by simulating the die-casting heating process (room temperature → 700℃, heating rate 100℃ / min). The results showed that after using the material of the present invention, the wear during the heating stage accounted for only 28% of the total wear (compared to as high as 62% for conventional ductile iron), proving that the present invention effectively solves the wear problem during the heating stage.

[0043] 5. Laser-quenched layer uniformity test

[0044] The results show that the material of the present invention (Example 1) has the best uniformity of hardened layer after laser surface quenching and no quenching cracks, proving that its alloy ratio is particularly suitable for laser quenching process.

[0045] in conclusion As can be seen from the above data, the material of the present invention (Example 1) is significantly superior to each comparative example in terms of thermal expansion matching, metallographic structure, hardness, laser quenching adaptability and service life, and achieves synergistic work with the H13 barrel, thus achieving the expected technical effect.

Claims

1. An aluminum alloy die-cast plunger material with a thermal expansion coefficient matching that of an H13 barrel, characterized in that, The chemical composition of the material, by weight percentage, is as follows: C 3.70%–3.75%, Si 1.80%–2.20%, Mn 0.60%–0.70%, P ≤0.04%, S ≤0.02%, Cr 0.30%–0.40%, Cu 0.70%–0.80%, Mo 0.25%–0.30%, Sb 0.005%–0.007%, with the balance being Fe and unavoidable impurities; the average coefficient of linear expansion of the material in the temperature range of 25℃–700℃ is 11.2 × 10⁻⁶. -6 / K~13.2×10 -6 / K, and the coefficient of thermal expansion of H13 mold steel in this temperature range deviates by ≤5%.

2. The aluminum alloy die-cast plunger material according to claim 1, characterized in that, The carbon equivalent (CE) of the material is controlled between 4.31 and 4.

50.

3. The aluminum alloy die-cast plunger material according to claim 1 or 2, characterized in that, The material has a cast pearlite content of ≥90%, and a pearlite content of ≥95% after normalizing treatment, and is free of free cementite and phosphine eutectic.

4. The aluminum alloy die-cast plunger material according to claim 1 or 2, characterized in that, After laser surface hardening, the surface hardness of the material reaches 52-58 HRC.

5. A method for preparing the aluminum alloy die-cast plunger material as described in any one of claims 1-4, characterized in that, Includes the following steps: Smelting: The raw materials are prepared according to the chemical composition of claim 1, and molten iron is obtained by smelting; Inoculation treatment: Inoculation treatment is carried out at the time of tapping. The inoculant is barium silicon or an equivalent inoculant, and the amount added is 0.4% to 0.6% of the weight of molten iron. Casting: Control the casting temperature to 1340~1390℃ to obtain the plunger head blank; Normalizing treatment: Normalizing the blank; Laser surface hardening: The working surface of the plunger head after normalizing is subjected to laser surface hardening. The laser power is 2.5 to 3.5 kW, the scanning speed is 200 to 400 mm / min, and the spot diameter is 3 to 5 mm.

6. The preparation method according to claim 5, characterized in that, The normalizing process is as follows: heat to 880℃~920℃, hold for 1.5~2.5 hours, and then air cool.

7. The preparation method according to claim 5, characterized in that, After laser surface quenching, the depth of the hardened layer is 1.0 to 1.5 mm, and the uniformity of the hardness of the hardened layer is controlled within ±2 HRC.

8. A plunger head for an aluminum alloy die-casting machine, characterized in that, Made from the material as described in any one of claims 1-4, or prepared by the method as described in any one of claims 5-7.

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