JP2004322112A - Hardened casting, manufacturing method, and method for hardening casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting having high mechanical properties even in the vicinity of a feeder head part without depending on a casting method for molding, and also, without depending on the solidification order during casting. <P>SOLUTION: The casting is characterized in that it is hardened by a dense layer formed on the surface side and the thickness of the dense layer is 300-2,000 μm. The casting is obtained by pouring molten metal into a mold. After that, a closed space, in which one surface is made as a constituent face, is formed at least on the one surface of the casting. The casting is oscillated after throwing a hardening material such as metal balls and cut wires into the closed space. As a result, the dense layer is formed on the front side of the casting. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００２８】しかし、マグネシウムとの混在でＭｇ_２Ｓｉとして析出して機械的性質を向上させるには一定の限界がある。又、ＡＣ２Ｂを除きＣｕの含有量は１．５質量％以下であり耐腐食性を有するが、一方、機械的性質を改善するには一定の限界がある。換言すれば、ＡＣ２Ｂ、ＡＣ３Ａ、ＡＣ４Ａ、ＡＣ４ＣＨ、ＡＣ４Ｄで示される鋳造用アルミニウム合金は従来の鋳物に用いられる場合には、図２（ａ）、図２（ｂ）に例示されたディーゼルエンジン用のシリンダヘッド２０に適う耐力及び硬度を付与するには必ずしも適切な材料ではなかった。
【００２９】本発明に係る第１の硬化鋳物によれば、ＡＣ４Ａ等の鋳造用アルミニウム合金の優位性（流動性、耐腐食性等）を生かしつつ、表面側に３００〜２０００μｍという従来にない厚さの緻密層が形成され硬化が図られているので、高い圧力に対してもクラック等が生じない。即ち、これらの鋳造用アルミニウム合金により作製された本発明に係る第１の硬化鋳物は、鋳造欠陥が少なく錆に強く、加えて、高い耐力と硬度を有する鋳物となり得る。
【００３０】次に、本発明に係る第２の硬化鋳物は、Ｓｉの含有率が１０質量％以下でありＣｕの含有率が２質量％以下である鋳造用アルミニウム合金を鋳造して得られる非熱処理の鋳物である。本発明に係る第２の硬化鋳物においては、０．２％耐力が１５０Ｎ／ｍｍ^２以上、且つ、硬度がブリネル硬度で７０ＨＢ以上又はマイクロビッカース硬度で７０ＨＶ以上であることを特徴とする。
【００３１】従来、Ｓｉの含有率が１０質量％以下でありＣｕの含有率が２質量％以下である鋳造用アルミニウム合金を用い、熱処理なしで得られる鋳物では、０．２％耐力で１４０Ｎ／ｍｍ^２、硬度では６９ＨＢ（ブリネル硬度）、又は６９ＨＶ（マイクロビッカース硬度）程度が上限であり、これはディーゼルエンジン用のシリンダヘッドとして適うものではなかった。
【００３２】Ｓｉの含有率が１０質量％を越える鋳造用アルミニウム合金（例えばＡＣ３ＡやＡＣ８Ａ（ＪＩＳ記号））を用いＭｇ_２Ｓｉの析出量を確保するか、又は、Ｃｕの含有率が２質量％を越える鋳造用アルミニウム合金（例えばＡＣ２ＢやＡＣ４Ｂ（ＪＩＳ記号））を用いることによれば、高い耐力と高い硬度を備えた鋳物を作製することは容易である。しかしながら、Ｓｉは入れ過ぎると強度向上の弊害になり、又、Ｃｕは入れ過ぎると耐腐食性を低下させる。従って、これらの含有量がより少ない鋳造用アルミニウム合金を用いて高い耐力と高い硬度を実現した鋳物が望まれていたが、従来は提供されていなかった。
【００３３】又、Ｓｉ及びＣｕの含有率が少ない鋳造用アルミニウム合金を用いた鋳物であっても熱処理すれば高い機械的性質を付与し得るが、熱処理に伴い製造コストも上昇し、市場に受け入れられ難くなる。従って、熱処理なしに一定以上高い耐力と高い硬度を備えた鋳物が得られることが望まれていた。
【００３４】本発明に係る第２の硬化鋳物は、後述する方法により鋳物に対する後処理として硬化が施されているので、Ｓｉの含有率が１０質量％以下でありＣｕの含有率が２質量％以下であっても、上記の如く、高い耐力と高い硬度を備えた鋳物になり得る。
【００３５】上記特徴を有する本発明に係る第１及び第２の硬化鋳物の好適な用途として、車両用部材、部品を挙げることが出来る。例えば、上記した図２（ａ）に側面の断面図が示され、図２（ｂ）シリンダ対向面２１が示されるディーゼルエンジン用のシリンダヘッド２０である。特に、高い圧縮比により高い圧力が生じ得るディ−ゼルエンジン周りの部品等として好適である。本発明に係る硬化鋳物の特徴を備えたこれら部品等は、高い耐力と高い硬度を備えることから、必要により狭小形状にならざるを得ない部品等であっても、長期にわたりクラック発生等の問題が生じず、ディ−ゼルエンジンの安定した継続運転を実現し、エンジンの信頼性向上に寄与する。
【００３６】続いて、本発明に係る鋳物の硬化方法について説明する。
【００３７】本発明に係る鋳物の硬化方法は、鋳物の表面側に緻密層を形成して鋳物を硬化する方法である。本発明に係る鋳物の硬化方法においては、鋳物の表面を構成面とする閉空間を形成し、閉空間内に硬化材を投入して鋳物を揺動させるところに特徴を有する。尚、本明細書において硬化とは硬度を向上させることを指す。
【００３８】本発明に係る鋳物の硬化方法においては、鋳物を形成する材料に適した硬さを有する硬化材を鋳物の表面を構成面とする空間に投入し、その空間を閉じて、以下に述べる好ましい揺れ幅、振動数、揺動時間で、鋳物を揺動させる。そうすると、硬化材が鋳物表面に対して衝突を繰り返し、鋳物に表面側から一定の厚さを有する緻密層が形成され、その結果、鋳物の硬度を向上させることが出来る。尚、本明細書において、振動数とは時間あたり繰り返される揺動の回数を指し、単位はヘルツ（Ｈｚ）である。
【００３９】従来のショットピーニング処理を施した場合には、鋳物は極表面の改質しか行われていなかったが、本発明に係る鋳物の硬化方法によれば、鋳物に表面側から３００〜２０００μｍの厚さの緻密層を形成することが可能である。
【００４０】又、本発明に係る鋳物の硬化方法では、成形した鋳物に対し後処理として厚い緻密層を形成するため、仮に鋳物の表面近傍に鋳造欠陥が存在していたとしても、厚い緻密層を形成する過程、即ち鋳物表面に対し硬化材が衝突を繰り返す工程を経ることによって、鋳造欠陥が修復されるという効果を発現する。従って、本発明に係る鋳物の硬化方法により硬化された鋳物の少なくとも表面側近傍には鋳造欠陥が皆無となり、いっそう高い硬度が付与されることになる。
【００４１】鋳物を揺動させるにあたり、硬化対象である鋳物の表面を構成面とする閉空間を形成し、その閉空間に硬化材を投入するが、閉空間は少なくとも硬化対象である表面を含む面に対し余裕空間を形成することが好ましい。余裕空間を形成しないと、閉空間端部まで硬化材が移動し難くなり、閉空間の端部において鋳物の表面に対する硬化材の衝突が不十分になって、硬化したい鋳物の表面側に所定の厚さの緻密層が形成出来なくなるからである。
【００４２】余裕空間を、図３に例示する。図３は、図２（ａ）、図２（ｂ）に示すシリンダヘッド２０のシリンダ対向面２１を構成するバルブシート２２部分を硬化対象としたとき、シリンダ対向面２１を囲い蓋３２で閉じたところを表す断面図である。囲い蓋３２により、バルブシート２２の直ぐ上部の空間の他に余裕空間３３を含む閉空間３１が形成されているので、シリンダヘッド２０を揺動させることによって、閉空間３１に投入された硬化材が両端にあるバルブシート２２の上部空間においても自由に運動し、バルブシート２２を含むシリンダ対向面２１の一定範囲の表面を均一に硬化し得る。尚、シリンダ対向面２１の全面を硬化対象とする場合には、シリンダ対向面２１の端部において硬化材を自由に運動させるため、余裕空間３３は、図示しないが、シリンダ対向面２１の端部より外れた外部空間として形成される。
【００４３】硬化材としては、少なくとも大きめの金属球若しくは金属球より極小なカットワイヤを含むことが好ましい。金属球若しくはカットワイヤを単独で用いてもよく、金属粒、研削剤乃至研磨剤、乾燥砂、等を混合し、２以上の混合物として、用いることも出来る。より好ましくは、少なくとも大きめの金属球を含む混合物である。又、大小の異なる金属球を用いることも好ましい。大きさの異なる硬化材を混在させることにより、それら硬化材が、より均一に漏れなく鋳物表面に対し衝突を繰り返すとともに、大きめの金属球により加圧され、鋳物の表面側の硬度を向上させ得るものと考えられる。
【００４４】金属球の径若しくはカットワイヤの長さ、あるいは、金属球若しくはカットワイヤを構成する材料は、鋳物を構成する材料、あるいは、鋳物の表面に形成する閉空間の高さ、等との相関により決定され、限定されるものではない。例えば、鋳物がアルミニウム合金からなるディーゼルエンジン用シリンダヘッドの場合には、φ１０〜２０ｍｍの鋼球乃至ステンレス球を好適に用いることが出来る。
【００４５】又、上記したような硬化材は、鋳物の表面に形成した閉空間の体積に対して、概ね５〜７０％の体積になるように投入することが好ましい。硬化材が閉空間の中で自由に動き、硬化材と鋳物表面との衝突回数が確保されることを担保するためである。５体積％未満では、硬化材は閉空間の中で自由に動くものの、鋳物表面の面積に対し硬化材が少なすぎる結果、硬化材と鋳物表面との衝突回数及び加圧力が確保されずに、鋳物の表面側に充分な厚さの緻密層が形成されず、好ましくない。７０体積％より多いと、硬化材が閉空間の中で自由に動く範囲が限定され、硬化材と鋳物表面との衝突回数及び加圧力が確保されずに、同様に鋳物の表面側に充分な厚さの緻密層が形成されず、好ましくない。
【００４６】以下、硬化材と鋳物表面とを衝突させるための鋳物の揺動について記載する。本発明は揺動条件を限定するものではないが、より好ましい条件としては、以下の通りである。
【００４７】振動数は、概ね５〜２０Ｈｚであることが好ましい。硬化材と鋳物表面との単位時間あたりの衝突回数を確保するためである。振動数が５Ｈｚ未満では、硬化材と鋳物表面との衝突回数が確保されず、硬化材が鋳物の表面全体において表面側に緻密層を形成しきれず、硬度が向上せず、好ましくない。又、硬化材（例えば鋼球）の数にもよるが、振動数が２０Ｈｚより多くても、硬度向上効果は小さく、振動数を上げるために費やすエネルギー対効果は低下するため、好ましくない。
【００４８】又、揺動の揺れ幅は、概ね３０〜２００ｍｍであることが好ましい。閉空間内での硬化材の移動範囲を適切に設定することを通して、硬化材と鋳物表面との単位時間あたりの衝突回数を確保するためである。揺れ幅が３０ｍｍ未満では、硬化材と鋳物表面との衝突回数が確保されず、硬化材が鋳物の表面全体において表面側に緻密層を形成しきれない結果、硬度が向上せず、好ましくない。又、揺れ幅が２００ｍｍより大きくても、硬化材が鋳物表面に接している時間が長くなるだけで、硬化材と鋳物表面との衝突回数は増加せず、硬度の向上効果は大きくはない。
【００４９】更には、揺動の延べ揺動時間は、概ね３〜１２０分であることが好ましい。硬化材と鋳物表面との延べ衝突回数を確保するためである。延べ揺動時間が３分未満では、硬化材と鋳物表面との延べ衝突回数が確保されず、硬化材が鋳物表面の全体において表面側に緻密層を形成しきれずに、硬度が充分に付与された部分と充分ではない部分とが存在してしまい、好ましくない。又、延べ揺動時間が１２０分より多くても、硬度の向上効果は小さく、鋳物製造にかかる時間対効果は向上しないため、好ましくない。
【００５０】本発明に係る鋳物の硬化方法においては、鋳物を揺動させる方向を、硬化材と鋳物表面との衝突回数が確保されるように、選定することが好ましい。それは硬化鋳物の閉空間の形状により異なる。例えば、図３に示すシリンダヘッド２０を揺動させる場合には、閉空間３１の長手方向、即ち、図３に示す矢印Ｑで示される方向に揺動させることは好ましくない。閉空間３１での移動距離が長くなる硬化材の比率が増えて、揺動による硬化材と鋳物表面との衝突回数が減じられるからある。シリンダヘッド２０を揺動させる場合に好ましい揺動方向は、例えば、図３に示す矢印Ｓで示される方向である。揺動中に方向を変えることも好ましい。
【００５１】本発明に係る鋳物の硬化方法は、鋳鉄若しくは鋳造用アルミニウム合金を主原料とする鋳物を対象とすることが好ましい。鋳造成形時において、湯流れや凝固収縮性がよい等の鋳造性に優れ鋳造欠陥が生じ難く、硬化を施すことにより、引張強さ、伸び、靱性等の機械的性質を、尚更に向上させることが出来るからである。
【００５２】鋳鉄とは、所定量の炭素を含む鉄−炭素合金をいう。鋳鉄の種類は限定されるものではないが、より優れる機械的性質を有する球状黒鉛鋳鉄を用いることが、より好ましい。鋳造用アルミニウム合金は、熱処理の有無、含有する他元素及びその組成比、等により種々存在するが、その種類は限定されるものではない。日本工業規格により、ＪＩＳ記号ＡＣ等で規定されているものを用いることが好ましく、ＡＣ２Ｂ、ＡＣ３Ａ、ＡＣ４Ａ、ＡＣ４ＣＨ、ＡＣ４Ｄ等を例示することが出来る。
【００５３】次に、本発明に係る鋳物硬化装置について説明する。
【００５４】本発明に係る鋳物硬化装置は、鋳物の表面側に緻密層を形成し、鋳物の表面を硬化する装置である。本発明に係る鋳物硬化装置においては、鋳物の表面を構成面とする閉空間を形成しその閉空間内に硬化材が投入された鋳物を任意の向きに固定し得る架台と、その架台を揺動させる揺動手段と、を有することに特徴がある。
【００５５】図７は、鋳物硬化装置の一実施形態を示す斜視図である。鋳物硬化装置７０は、揺動手段７４と、閉空間が形成され閉空間内に硬化材が投入された鋳物を載せる架台７３とから構成される。揺動手段７４は原動機７１と、原動機７１に接続されたクランク７２からなり、原動機７１による回転運動をクランク７２で往復運動に変え、架台７３を矢印Ｓ２方向に揺動させることが出来る。架台７３はの形状は限定されない。鋳物の形状と揺動方向とが固定されている場合には、特定の形状を呈してもよいが、平板でも構わず、鋳物を任意の向きに固定出来ればよい。
【００５６】例えば、図３に示すシリンダヘッド２０を、鋳物硬化装置７０を用いて揺動させるには、閉空間３１に所定の硬化材を投入したシリンダヘッド２０を、鋳物硬化装置７０の揺動方向である矢印Ｓ２方向に対して、矢印Ｓ方向（図３）とが一致するように、架台７３に固定して、原動機７１を稼動させればよい。
【００５７】続いて、本発明に係る硬化鋳物の製造方法について説明する。
【００５８】本発明に係る硬化鋳物の製造方法は、表面側に形成された緻密層により硬化された鋳物を製造する方法である。本発明に係る硬化鋳物の製造方法においては、鋳型内に溶湯を注入して鋳造成形し鋳物を得た後に、鋳物の少なくとも一表面において、その一表面を構成面とする閉空間を形成し、その閉空間内に硬化材を投入して鋳物を揺動させ、一表面を含む鋳物の表面側に緻密層を形成するところに特徴がある。そして、本発明に係る硬化鋳物の製造方法は、好ましくは、緻密層を形成する前又は後において熱処理を施す。鋳造成形に用いる鋳型は、砂型、金型等何れでもよく、又、鋳造法は、その手段を限定するものではなく、重力鋳造法、ダイカスト法や低圧鋳造法を含み、所定形状のキャビティを有する鋳型に溶融した金属（溶湯）を注入し成形する方法であればよい。
【００５９】本発明に係る硬化鋳物の製造方法は、図１（ａ）に示されるように、少なくとも鋳造工程１と硬化処理工程２を有し、好ましくは熱処理工程３を有する。これら工程を含む製造方法の概略は次の通りである。先ず、所定の材料を原料として用意し、溶解して溶湯を得た後に、必要に応じ溶湯に清浄化処理を施す。そして、溶湯を鋳型へ注ぎ、冷却等により成形する（鋳造工程１）。次いで、得られた成形体（鋳物）に発生したバリ等を除去し外側の形状を整える。そして、鋳物の一表面を構成面として閉空間を形成し、例えば金属球と金属粒からなる硬化材を投入して鋳物を揺動させて、鋳物の表面側に所定の厚さの緻密層を設け硬度を付与する（硬化処理工程２）。その後、例えばＴ６処理等を施して、鋳物の機械的性質を向上させる（熱処理工程３）。
【００６０】本発明に係る硬化鋳物の製造方法は、図１（ｂ）に示されるように、熱処理工程３を硬化処理工程２の前に行ってもよい。即ち、緻密層を設けることによる機械的性質の向上と、熱処理による機械的性質の向上とは、作用効果を異とするため各々独立して行い得る。より好ましくは、硬化処理工程２を先に行う。又、熱処理はＴ５処理やＴ７処理でもよく、限定されない。熱処理は行わなくてもよい。
【００６１】更には、図１（ｃ）に示されるように、少なくとも硬化処理工程２を終えた後に、平坦化処理工程４を行うことが好ましい場合がある。硬化処理は硬化材を鋳物表面に衝突させる処理であるため、硬化処理された鋳物の表面は表面粗さが非常に小さい滑らかな面になり得るが、一方、底部と頂部の差が極小さい凹凸が確認される。例えばシリンダヘッドのシリンダ対向面を硬化させる場合にはシリンダ対向面がシリンダと接合する面となるが、この例のように、硬化処理を施す面が別の面と接合する面になるときは、極僅かであるが凹凸のついた面では好ましくないことがある。この場合、例えば、フライス加工等による平坦化処理を施すことにより密着して接合させることが出来る。平坦化処理を施しても、硬化された鋳物に形成された緻密層は所定の厚さを有することから、硬度を低下させることがない。
【００６２】
【実施例】次に、本発明を実施例に基づき更に詳細に説明するが、本発明はこれらの実施例に限られるものではない。
【００６３】鋳物として、Ｖ型６気筒ディーゼルエンジン用のシリンダヘッドを、アルミニウム合金（ＡＣ４ＣＨ）を原料として鋳造法により成形し、６体用意した（シリンダヘッドＡ〜Ｆとする）。シリンダヘッドの形状は図２（ａ）、図２（ｂ）に示される如く複雑な孔部が形成された概ね矩形体である。
【００６４】成形された６体のシリンダヘッドのうち３体（シリンダヘッドＡ，Ｂ，Ｃとする）について、シリンダ対向面のバルブシートを硬化対象として閉空間を形成し（図３参照）、この閉空間の中へ硬化材としてφ１５ｍｍの鋼球とφ１０ｍｍの鋼球とを投入し、振動数８Ｈｚ、揺れ幅６０ｍｍで揺動させ、シリンダ対向面のバルブシート部分の硬化処理を施した。又、揺動方向は、シリンダヘッドに対し概ね垂直方向（図３中の矢印Ｓで示す方向）とした。尚、成形された６体のシリンダヘッドのうちシリンダヘッドＤ，Ｅ，Ｆについては硬化処理は施していない。
【００６５】シリンダヘッドＡ〜Ｆから、吸気ポート２８と排気ポート２９との間のバルブシート２２（図２（ｂ）参照）を含む試験片を４体ずつ切り出した。そして、各試験片について以下の通り、引張試験、及び、硬度試験を行った。
【００６６】（引張試験）
【００６７】シリンダヘッドＡから得た試験片のうち３体（実施例１〜３）及びシリンダヘッドＤから得た試験片のうち３体（比較例１〜３）を用いて引張試験を行い、機械的性質（引張強さ、０．２％耐力、伸び）を測定した。結果を図４に示す。尚、引張試験は日本工業規格に基づいて行った。
【００６８】（硬度試験その１）
【００６９】シリンダヘッドＢから得た試験片４体（実施例４〜７）及びシリンダヘッドＥから得た試験片４体（比較例４〜７）を用いて、各試験片に対して、表面から４０μｍの深さの部分と、表面から２０００μｍの深さの部分とを対象にそれぞれマイクロビッカース硬度試験を行い、硬度を測定した。結果を表２に示す。尚、マイクロビッカース硬度試験は日本工業規格に基づいて行った。
【００７０】
【表２】

【００７１】（硬度試験その２）
【００７２】上記実施例４で使用した試験片に対して、上記硬度試験その１とは別の部分で、表面から深さ３ｍｍまでを対象にマイクロビッカース硬度試験を行い、硬度を測定した。結果を図６に示す。尚、表面から深さ０．５ｍｍまでは５０μｍ毎に、深さ０．５ｍｍを越えてから深さ１．５ｍｍまでは１００μｍ毎に、深さ１．５ｍｍを越えてからは２００μｍ毎に、硬度試験を行った。
【００７３】（硬度試験その３）
【００７４】シリンダヘッドＣから得た試験片のうち３体（実施例８〜１０）及びシリンダヘッドＦから得た試験片のうち３体（比較例８〜１０）を用いてブリネル硬度試験を行い、硬度を測定した。結果を図５に示す。尚、ブリネル硬度試験は日本工業規格に基づいて行った。
【００７５】
【発明の効果】以上説明したように、本発明によれば、表面側に厚さが３００〜２０００μｍである緻密層が形成された硬化鋳物、乃至は、Ｓｉの含有率が１０質量％以下でありＣｕの含有率が２質量％以下である鋳造用アルミニウム合金を鋳造して得られる非熱処理の鋳物であって、０．２％耐力が１５０Ｎ／ｍｍ^２以上、且つ、硬度がブリネル硬度で７０ＨＢ以上又はマイクロビッカース硬度で７０ＨＶ以上である硬化鋳物が提供される。これら硬化鋳物は、狭小形状をなす部分があって、そこへ高い圧力がかかっても、クラックの発生等の問題が生じ難いため、例えばディーゼルエンジン用のシリンダヘッドに好適に採用され、安定継続運転を通じてディーゼルエンジンの信頼性向上に寄与する。
【００７６】又、本発明によれば、鋳物に対する後処理として、一定の厚さを有する緻密層を形成し硬度を向上させる鋳物の硬化方法、及び、その硬化方法を含む鋳物の製造方法が提供される。従って、鋳物を得るための鋳造法によらず生産性の高い方法を選んで優れた硬度の鋳物を得ることが出来る。又、例えば鋳物の鋳造時の押湯部近傍であっても、優れた硬度を付与することが可能であるため、押湯部を大きくする等により歩留まりを低下させることがない。
【図面の簡単な説明】
【図１】本発明に係る硬化鋳物の製造方法の一例を示す図であり、図１（ａ）、図１（ｂ）、図１（ｃ）は製造工程のブロックフロー図である。
【図２】鋳物の一例であるディ−ゼルエンジン用シリンダヘッドを示す図であり、図２（ａ）はシリンダ対向面を下方とした場合の側面の断面図を示し、図２（ｂ）は図２（ａ）において図中の下方から見た図であり、シリンダ対向面を表す図である。
【図３】本発明に係る鋳物の硬化方法の一実施形態を示す断面図であり、鋳物の一例であるシリンダヘッドのシリンダ対向面に囲い蓋によって閉空間を形成したところを示す図である。
【図４】実施例における引張試験の結果を示すグラフである。
【図５】実施例におけるブリネル硬度試験の結果を示すグラフである。
【図６】実施例におけるマイクロビッカース硬度試験の結果を示すグラフである。
【図７】本発明に係る鋳物硬化装置の一実施形態を示す斜視図である。
【符号の説明】
１…鋳造工程、２…硬化処理工程、３…熱処理工程、４…平坦化処理工程、２０…シリンダヘッド、２１…シリンダ対向面、２２…バルブシート、２３…バルブ２８…吸気ポート、２９…排気ポート、３１…閉空間、３２…囲い蓋、３３…余裕空間。[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting in which a dense layer having a certain thickness is formed on the surface side and hardened by forming the dense layer.
[0002]
2. Description of the Related Art Castings obtained by placing a molten metal (molten metal) in a mold and cooling and molding are applied to various uses because of a relatively simple manufacturing method. Depending on the properties to be used and the metal material used as a raw material or the casting method used, a problem may occur.
For example, in order to suppress global warming, which is one of the global environmental problems, there is a strong worldwide demand for reduction of automobile fuel consumption, which leads to carbon dioxide emission. Lightening materials that contribute to improved fuel economy are used for parts and members that are made of such materials. Among them, castings made of aluminum (Al) alloy material, which is relatively inexpensive, are used, for example, parts around the engine and around the feet. Has been adopted as many.
[0004] These automobile parts are required to have higher mechanical properties because they are directly linked to safety and reliability. Therefore, in general, it is difficult to adopt a die casting method which is excellent in productivity but difficult to produce a high strength casting method. In addition, the gravity casting method has a low productivity and a high cost of the casting, so that the production target is limited.
[0005] Low-pressure casting is a relatively preferred casting in terms of the balance between mechanical properties and productivity obtained. However, even when this method is employed, since the vicinity of the feeder is solidified lastly, internal casting defects such as shrinkage holes and pores are likely to gather and mechanical properties are likely to be reduced. There is a demand for providing high mechanical properties, and there is a problem that it cannot be met. Increasing the size of the feeder can solve the problem of reduced mechanical properties, but the yield is reduced and the casting becomes incompetitive and is hardly accepted in the market.
The above problem will be described with a specific example. 2 (a) and 2 (b) show a portion near an intake port / exhaust port of a cylinder head for a diesel engine as an example of a cast automobile part or the like. For example, when the cylinder head 20 for a diesel engine is manufactured by a low-pressure casting method, in order to stabilize the holding of the core and prevent the occurrence of shrinkage cavities, the cylinder facing surface 21 is in the vicinity of the feeder, that is, Since a portion close to the portion that finally solidifies is formed, the mechanical properties are likely to deteriorate. On the other hand, in a diesel engine, light oil is injected into air heated to a high temperature by high compression without ignition, and spontaneous ignition occurs. Therefore, high pressure is applied to the cylinder facing surface 21. As a result, for example, there has been a problem that a crack occurs in the valve seat 22 between the narrow intake port 28 and the narrow exhaust port 29 (opening portion where the valve 23 opens and closes).
Conventionally, as a means for improving the mechanical properties of a casting, a shot peening process, which is post-processing of the casting, is known (application techniques of shot peening are disclosed, for example, in Patent Documents 1 to 4). ing). The shot peening process, as described in Patent Document 1, is to project small particles at high speed to plastically deform only the outer surface of the material to be processed, to generate compressive residual stress, and to increase mechanical strength. Technology to improve.
However, even if this shot peening process is performed on the cylinder facing surface 21 of the cylinder head 20, for example, the problem of cracks in the valve seat 22 is not solved. The reason for this is that the object to be treated is limited only to the surface of the material to be treated, so that the property of the surface of the material to be treated is rather deteriorated, as described in Patent Document 2. More specifically, casting defects such as oxide films existing near the surface are made apparent. Also, the treatment does not have the effect of crushing near-surface defects that may be caused by hydrogen gas released during solidification. Naturally, the desired mechanical properties cannot be obtained.
[0009]
[Patent Document 1]
Japanese Patent Publication No. 8-11366
[Patent Document 2]
Japanese Patent No. 3225066
[Patent Document 3]
Japanese Patent No. 312433
[Patent Document 4]
JP 2001-138030 A
[0010]
As described above, the conventional problems have been described by exemplifying a cylinder head for a diesel engine as a casting, but the present invention has been made in view of these problems, and an object thereof is to be solved. However, it is an object of the present invention to provide a casting that can provide high mechanical properties regardless of a casting method for molding and regardless of a solidification sequence at the time of casting, even in the vicinity of a feeder.
As a result of repeated studies on means for imparting high mechanical properties to the casting, the casting method after molding is more improved than the improvement and review of the selection of the casting method and the manufacturing method including the selected casting method. As a result of repeated research based on the policy that new means for post-processing should be developed, the following means that can replace the conventional shot peening processing, and the castings obtained by the following means, have been Has been found to be achieved.
[0012]
That is, according to the present invention, there are provided the following two hardened castings. The first hardened casting is a casting hardened by the dense layer formed on the surface side, and the thickness of the dense layer is 300 to 2000 μm. The first hardened casting is formed by casting any one material selected from a group of aluminum alloy materials for casting including AC2B, AC3A, AC4A, AC4CH, and AC4D or a material in which two or more are mixed as a main raw material. Is preferred.
According to the present invention, there is provided a non-casting aluminum alloy obtained by casting a silicon (Si) content of not more than 10% by mass and a copper (Cu) content of not more than 2% by mass. A heat-treated casting with a 0.2% proof stress of 150 N / mm ² As described above, a second hardened casting having a hardness of 70 HB or more in Brinell hardness or 70 HV or more in Micro Vickers hardness is provided.
A cylinder head for a diesel engine is preferable as the first and second hardened castings. Such a cylinder head for a diesel engine solves the conventional problem and can prevent the occurrence of cracks in the valve seat under high pressure.
Further, according to the present invention, there is provided a method for producing a casting hardened by a dense layer formed on the surface side, wherein a molten metal is poured into a mold to form a casting. On at least one surface, a closed space having the one surface as a constituent surface is formed, a hardening material is injected into the closed space to swing the casting, and a dense layer is formed on the surface side of the casting including the one surface A method for producing a hardened casting is provided. In the method for producing a hardened casting according to the present invention, it is preferable to perform a heat treatment before or after forming the dense layer. Although the heat treatment is not limited, for example, T5 treatment, T6 treatment, T7 treatment and the like can be mentioned.
The method for producing a hardened casting according to the present invention preferably includes a step of forming a dense layer and then performing a flattening treatment on the surface of the casting including one surface. Due to the introduction of the hardening material and the swing of the casting, the surface of the casting is smoothed and the surface roughness is improved, but very slight unevenness is formed. May be required. Note that the planarization treatment may be performed before or after the heat treatment.
Further, according to the present invention, there is provided a method for forming a dense layer on the surface side of a casting and hardening the casting, wherein a closed space having the surface of the casting as a constituent surface is formed, and a hardening material is formed in the closed space. And a method for hardening a casting, characterized in that the casting is rocked by feeding the casting.
In the method for hardening a casting according to the present invention, the oscillation frequency is preferably about 5 to 20 Hz, and the oscillation width is preferably about 30 to 200 mm. It is preferable that the total swing time of the swing is approximately 3 to 120 minutes.
The amount of the hardening material to be added is preferably about 5 to 70% by volume relative to the closed space, and the hardening material is a mixture of at least one or more containing metal spheres or cut wires, It is preferable that
The method of hardening a casting according to the present invention is suitable when the main material constituting the casting is cast iron or an aluminum alloy for casting.
According to the present invention, there is provided an apparatus for forming a dense layer on the surface side of a casting and hardening the surface of the casting, wherein a closed space having the surface of the casting as a constituent surface is formed and hardened in the closed space. There is provided a casting hardening device, comprising: a gantry capable of fixing a casting into which a material has been put in an arbitrary direction; and a swinging means for swinging the gantry. In the casting hardening device according to the present invention, it is preferable that the oscillating means has a motor and a crank connected to the motor.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a hardened casting, a method of manufacturing the same, and a method of hardening a casting according to the present invention will be described in detail, but the present invention should not be construed as being limited thereto. Rather, various changes, modifications, and improvements may be made based on the knowledge of those skilled in the art without departing from the scope of the present invention. In this specification, the term “hardened casting” or “casting according to the present invention” refers to both the first hardened casting and the second hardened casting.
In the present invention, a casting refers to a metal molded body obtained by a casting method, and the casting method used is not limited. That is, die casting is also included in the casting. Further, the denseness of the dense layer formed in the casting indicates the relative denseness of the metal structure, and the dense layer formed on the surface side is relative to the metal structure inside the casting formed on the surface side. A layer that is dense in nature. The surface side refers to a portion including the surface and a certain depth from the surface, and indicates that the dense layer is formed not only at the extreme surface but also at a predetermined thickness. Furthermore, the casting according to the present invention is not limited to being composed of two layers of a dense layer and a non-dense layer (referred to as a coarse-grained layer) inside the casting, and the relative densities of the metal structures are different. It may be formed of three or more layers.
First, the hardened casting according to the present invention will be described. The hardened casting according to the present invention is composed of first and second castings.
The first hardened casting according to the present invention is a casting which is a molded article formed by a casting method, and has a dense layer formed on the surface side and is hardened by the dense layer. The first hardened casting according to the present invention is characterized in that the dense layer has a thickness of 300 to 2000 μm. A hardened casting having a thick dense layer, which is not found in a conventional shot-peened casting having a thickness of 300 to 2000 μm, has higher mechanical properties than the conventional one, specifically, higher proof stress and hardness. Thus, even if a high pressure is applied, problems such as cracks do not occur. Further, as shown in a manufacturing method (or a curing method) described later, the formation of a dense layer having a thickness of 300 to 2000 μm repairs casting defects and eliminates casting defects at least near the surface side. From this, a casting having better mechanical properties than before can be obtained. Further, since it is a casting, it can be formed into a desired shape by a mold.
The first hardened casting according to the present invention is any one of a material or a material selected from the group of aluminum alloy materials for casting indicated by JIS (Japanese Industrial Standard) symbols AC2B, AC3A, AC4A, AC4CH, AC4D. It can be obtained by casting a material in which the above is mixed as a main raw material. These casting aluminum alloys whose chemical component values are shown in Table 1 have an appropriate amount of Si and have preferable fluidity, and have excellent castability such as good melt flow and solidification shrinkage during casting. It is an excellent material that hardly causes casting defects such as shrinkage cavities.
[0027]
[Table 1]

However, when mixed with magnesium, Mg ₂ There is a certain limit in precipitating as Si and improving the mechanical properties. Except for AC2B, the content of Cu is 1.5% by mass or less and has corrosion resistance, but there is a certain limit in improving mechanical properties. In other words, when the casting aluminum alloys represented by AC2B, AC3A, AC4A, AC4CH, and AC4D are used in conventional castings, the aluminum alloys for diesel engines illustrated in FIGS. 2 (a) and 2 (b) are used. The material is not always suitable for providing the proof stress and hardness suitable for the cylinder head 20.
According to the first hardened casting of the present invention, the unprecedented thickness of 300 to 2000 μm is provided on the surface side while taking advantage of the superiority (fluidity, corrosion resistance, etc.) of a casting aluminum alloy such as AC4A. Since a dense layer is formed and hardened, cracks and the like do not occur even under a high pressure. That is, the first hardened casting according to the present invention made of these casting aluminum alloys can be a casting having few casting defects, being resistant to rust, and having high proof stress and hardness.
Next, the second hardened casting according to the present invention is obtained by casting a casting aluminum alloy having a Si content of 10% by mass or less and a Cu content of 2% by mass or less. It is a casting of heat treatment. In the second hardened casting according to the present invention, the 0.2% proof stress is 150 N / mm. ² The hardness is 70 HB or more in Brinell hardness or 70 HV or more in micro Vickers hardness.
Conventionally, a casting obtained by using an aluminum alloy for casting having a Si content of 10% by mass or less and a Cu content of 2% by mass or less without heat treatment has a 0.2% proof stress of 140 N / mm ² The upper limit of the hardness was about 69HB (Brinell hardness) or 69HV (micro Vickers hardness), which was not suitable as a cylinder head for a diesel engine.
Using an aluminum alloy for casting (for example, AC3A or AC8A (JIS symbol)) having a Si content exceeding 10% by mass, ₂ According to securing the precipitation amount of Si or using an aluminum alloy for casting (for example, AC2B or AC4B (JIS symbol)) in which the Cu content exceeds 2% by mass, a high yield strength and a high hardness are provided. It is easy to make a casting. However, if Si is added too much, it will hurt the strength improvement, and if Cu is added too much, the corrosion resistance will be reduced. Therefore, castings having high yield strength and high hardness using casting aluminum alloys with lower contents thereof have been desired, but have not been provided so far.
Further, even if the casting is made of an aluminum alloy for casting having a low content of Si and Cu, high mechanical properties can be imparted by heat treatment. It will be difficult to be. Accordingly, it has been desired to obtain a casting having high yield strength and high hardness over a certain level without heat treatment.
Since the second hardened casting according to the present invention has been hardened as a post-treatment of the casting by the method described later, the content of Si is 10% by mass or less and the content of Cu is 2% by mass. Even if it is the following, as described above, a casting having high proof stress and high hardness can be obtained.
Suitable applications of the first and second hardened castings according to the present invention having the above characteristics include members and parts for vehicles. For example, FIG. 2A shows a cross-sectional side view, and FIG. 2B shows a cylinder head 20 for a diesel engine in which a cylinder facing surface 21 is shown. In particular, it is suitable as a part around a diesel engine, which can generate high pressure due to a high compression ratio. Since these parts and the like having the characteristics of the hardened casting according to the present invention have high proof stress and high hardness, even if the parts have to be formed into a narrow shape as necessary, problems such as crack generation for a long period of time may occur. Does not occur, and realizes stable continuous operation of the diesel engine, contributing to the improvement of engine reliability.
Next, a method for hardening a casting according to the present invention will be described.
The method for hardening a casting according to the present invention is a method for hardening a casting by forming a dense layer on the surface side of the casting. The method for hardening a casting according to the present invention is characterized in that a closed space having the surface of the casting as a constituent surface is formed, and a hardening material is injected into the closed space to swing the casting. In addition, in this specification, hardening means improving hardness.
In the method for hardening a casting according to the present invention, a hardening material having a hardness suitable for a material forming the casting is charged into a space having the surface of the casting as a constituent surface, and the space is closed. The casting is rocked with the preferred rocking width, frequency and rocking time described. Then, the hardened material repeatedly collides with the casting surface, and a dense layer having a certain thickness is formed on the casting from the surface side. As a result, the hardness of the casting can be improved. In addition, in this specification, the frequency refers to the number of times of repetition of oscillation per time, and the unit is hertz (Hz).
When the conventional shot peening treatment is performed, the casting is only modified on the very surface. However, according to the casting hardening method according to the present invention, the casting is 300 to 2000 μm from the surface side. It is possible to form a dense layer having a thickness of
In the method for hardening a casting according to the present invention, a thick dense layer is formed as a post-process on the molded casting, so that even if casting defects exist near the surface of the casting, the thick dense layer is formed. , That is, a step of repeating the collision of the hardening material with the surface of the casting, thereby producing an effect of repairing the casting defect. Therefore, there is no casting defect at least in the vicinity of the surface side of the casting hardened by the casting hardening method according to the present invention, and higher hardness is provided.
In swinging the casting, a closed space is formed having the surface of the casting to be hardened as a constituent surface, and a hardening material is introduced into the closed space. The closed space includes at least the surface to be hardened. It is preferable to form an extra space for the surface. If the spare space is not formed, the hardened material is difficult to move to the end of the closed space, and the hardened material does not sufficiently collide with the surface of the casting at the end of the closed space. This is because a dense layer having a thickness cannot be formed.
FIG. 3 shows an example of the extra space. 3A and 3B, when the valve seat 22 constituting the cylinder facing surface 21 of the cylinder head 20 shown in FIGS. 2A and 2B is to be cured, the cylinder facing surface 21 is closed with a lid 32. It is sectional drawing showing a place. Since the closed space 31 including the extra space 33 is formed by the surrounding lid 32 in addition to the space immediately above the valve seat 22, the hardening material put into the closed space 31 by swinging the cylinder head 20. Can freely move even in the upper space of the valve seat 22 at both ends, and can uniformly cure the surface of a certain range of the cylinder facing surface 21 including the valve seat 22. When the entire surface of the cylinder facing surface 21 is to be cured, the hardening material can freely move at the end of the cylinder facing surface 21. It is formed as a more external space.
The hardening material preferably contains at least a large metal sphere or a cut wire smaller than the metal sphere. A metal ball or a cut wire may be used alone, or a mixture of two or more metal particles, abrasives or abrasives, dry sand, or the like may be used. More preferably, it is a mixture containing at least larger metal spheres. It is also preferable to use metal balls of different sizes. By mixing hardening materials having different sizes, the hardening materials can be more evenly repeated against the casting surface without leakage, and can be pressed by a large metal ball to improve the hardness of the casting surface side. It is considered.
The diameter of the metal sphere or the length of the cut wire, or the material forming the metal sphere or the cut wire is determined by the material forming the casting or the height of a closed space formed on the surface of the casting. It is determined by correlation and is not limited. For example, in the case of a cylinder head for a diesel engine whose casting is made of an aluminum alloy, a steel ball or a stainless steel ball of φ10 to 20 mm can be preferably used.
It is preferable that the above-mentioned hardening material is introduced so as to have a volume of about 5 to 70% of the volume of the closed space formed on the surface of the casting. This is to ensure that the hardening material freely moves in the closed space and that the number of collisions between the hardening material and the casting surface is ensured. When the volume is less than 5% by volume, the hardening material moves freely in the closed space, but the hardening material is too small with respect to the area of the casting surface, so that the number of collisions between the hardening material and the casting surface and the pressing force are not secured. A dense layer having a sufficient thickness is not formed on the surface side of the casting, which is not preferable. If the amount is more than 70% by volume, the range in which the hardening material freely moves in the closed space is limited, and the number of collisions between the hardening material and the casting surface and the pressing force are not ensured. A dense layer having a thickness is not formed, which is not preferable.
Hereinafter, the swing of the casting for causing the hardened material to collide with the casting surface will be described. Although the present invention does not limit the swing condition, more preferred conditions are as follows.
The frequency is preferably about 5 to 20 Hz. This is for ensuring the number of collisions between the hardened material and the casting surface per unit time. When the vibration frequency is less than 5 Hz, the number of collisions between the hardened material and the casting surface is not secured, and the hardened material cannot form a dense layer on the entire surface of the casting, and the hardness is not improved, which is not preferable. Further, although it depends on the number of hardening materials (for example, steel balls), it is not preferable that the frequency is higher than 20 Hz because the effect of improving the hardness is small and the effect on energy used to increase the frequency is reduced.
Further, the swing width of the swing is preferably about 30 to 200 mm. This is to secure the number of collisions between the hardened material and the casting surface per unit time by appropriately setting the moving range of the hardened material in the closed space. If the swing width is less than 30 mm, the number of collisions between the hardened material and the surface of the casting is not ensured, and the hardened material cannot form a dense layer on the entire surface of the casting, resulting in an increase in hardness, which is not preferable. Further, even if the swing width is larger than 200 mm, only the time during which the hardened material is in contact with the casting surface is increased, the number of collisions between the hardened material and the casting surface is not increased, and the effect of improving the hardness is not significant.
Further, the total swing time of the swing is preferably about 3 to 120 minutes. This is to ensure the total number of collisions between the hardened material and the casting surface. If the total oscillating time is less than 3 minutes, the total number of collisions between the hardened material and the casting surface is not secured, and the hardened material cannot fully form a dense layer on the surface side of the entire casting surface, and sufficient hardness is provided. This is not preferable because there are portions that are not enough and portions that are not enough. Further, if the total swinging time is longer than 120 minutes, the effect of improving the hardness is small, and the effect on the time required for casting production is not improved, which is not preferable.
In the method for hardening a casting according to the present invention, it is preferable to select the direction in which the casting is rocked so that the number of collisions between the hardened material and the casting surface is ensured. It depends on the shape of the closed space of the hardened casting. For example, when the cylinder head 20 shown in FIG. 3 is swung, it is not preferable to swing the cylinder head 20 in the longitudinal direction of the closed space 31, that is, in the direction indicated by the arrow Q shown in FIG. This is because the ratio of the hardening material having a longer moving distance in the closed space 31 increases, and the number of collisions between the hardening material and the casting surface due to swinging is reduced. A preferred swing direction for swinging the cylinder head 20 is, for example, a direction indicated by an arrow S shown in FIG. It is also preferable to change the direction during rocking.
The method for hardening a casting according to the present invention is preferably applied to a casting mainly made of cast iron or a casting aluminum alloy. During casting, it is excellent in castability such as good flow of molten metal and solidification shrinkage, hardly causes casting defects, and by hardening, mechanical properties such as tensile strength, elongation and toughness are further improved. Is possible.
[0052] Cast iron is an iron-carbon alloy containing a predetermined amount of carbon. Although the type of cast iron is not limited, it is more preferable to use spheroidal graphite cast iron having more excellent mechanical properties. There are various types of aluminum alloys for casting depending on the presence or absence of heat treatment, other elements to be contained and the composition ratio thereof, but the type is not limited. According to the Japanese Industrial Standards, it is preferable to use those specified by the JIS symbol AC or the like, and examples thereof include AC2B, AC3A, AC4A, AC4CH, and AC4D.
Next, the casting hardening apparatus according to the present invention will be described.
The casting hardening apparatus according to the present invention is an apparatus for forming a dense layer on the surface side of a casting and hardening the casting surface. In the casting hardening apparatus according to the present invention, a gantry capable of forming a closed space having the surface of the casting as a constituent surface and fixing the casting in which the hardening material is charged in the closed space in an arbitrary direction, and shaking the gantry. And a rocking means for moving.
FIG. 7 is a perspective view showing an embodiment of a casting hardening device. The casting hardening device 70 includes a swinging means 74 and a pedestal 73 on which a closed space is formed and a casting in which a hardening material is charged is placed. The oscillating means 74 includes a motor 71 and a crank 72 connected to the motor 71. The rotating motion of the motor 71 is changed into a reciprocating motion by the crank 72, and the gantry 73 can be rocked in the direction of arrow S2. The shape of the gantry 73 is not limited. When the shape of the casting and the swing direction are fixed, the casting may have a specific shape, but may be a flat plate, as long as the casting can be fixed in any direction.
For example, in order to swing the cylinder head 20 shown in FIG. 3 using the casting hardening device 70, the cylinder head 20 in which a predetermined hardening material is charged into the closed space 31 is swung. The prime mover 71 may be operated while being fixed to the gantry 73 such that the direction of the arrow S (FIG. 3) coincides with the direction of the arrow S2.
Next, a method for producing a hardened casting according to the present invention will be described.
The method for producing a hardened casting according to the present invention is a method for manufacturing a hardened casting by a dense layer formed on the surface side. In the method for producing a hardened casting according to the present invention, after casting a molten metal in a mold and casting to obtain a casting, at least one surface of the casting, forming a closed space having one surface as a constituent surface, It is characterized in that a hardening material is introduced into the closed space to swing the casting, and a dense layer is formed on the surface side of the casting including one surface. In the method for producing a hardened casting according to the present invention, heat treatment is preferably performed before or after forming the dense layer. The mold used for casting may be a sand mold, a mold, or the like, and the casting method is not limited to any means, and includes a gravity casting method, a die casting method and a low pressure casting method, and has a cavity of a predetermined shape. Any method may be used as long as it is a method in which a molten metal (molten metal) is injected into a mold and molded.
As shown in FIG. 1A, the method for producing a hardened casting according to the present invention includes at least a casting step 1 and a hardening step 2, preferably a heat treatment step 3. The outline of the manufacturing method including these steps is as follows. First, a predetermined material is prepared as a raw material, and after melting to obtain a molten metal, the molten metal is subjected to a cleaning treatment as necessary. Then, the molten metal is poured into a mold and molded by cooling or the like (casting process 1). Next, burrs and the like generated on the obtained molded body (casting) are removed and the outer shape is adjusted. Then, a closed space is formed with one surface of the casting as a constituent surface, for example, a hardening material consisting of metal balls and metal grains is charged and the casting is rocked, and a dense layer of a predetermined thickness is formed on the surface side of the casting. The provided hardness is provided (hardening treatment step 2). Then, the mechanical properties of the casting are improved by, for example, T6 treatment (heat treatment step 3).
In the method for producing a hardened casting according to the present invention, the heat treatment step 3 may be performed before the hardening step 2 as shown in FIG. That is, the improvement of the mechanical properties by providing the dense layer and the improvement of the mechanical properties by the heat treatment can be performed independently of each other because they have different effects. More preferably, the curing step 2 is performed first. The heat treatment may be a T5 treatment or a T7 treatment, and is not limited. Heat treatment may not be performed.
Further, as shown in FIG. 1C, it may be preferable to perform the flattening process 4 at least after the hardening process 2 is completed. Since the hardening process is a process in which the hardening material collides with the casting surface, the surface of the hardened casting can be a smooth surface with a very small surface roughness, while the difference between the bottom and the top is very small. Is confirmed. For example, when the cylinder facing surface of the cylinder head is cured, the cylinder facing surface is a surface to be joined to the cylinder, but as in this example, when the surface to be cured becomes a surface to be joined to another surface, A very slight but uneven surface may not be preferable. In this case, for example, by performing a flattening process by milling or the like, it is possible to make close contact and join. Even when the flattening treatment is performed, the dense layer formed on the hardened casting has a predetermined thickness, so that the hardness does not decrease.
[0062]
Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
As a casting, six cylinder heads for a V-type six-cylinder diesel engine were formed by casting using an aluminum alloy (AC4CH) as a raw material, and six cylinder heads were prepared (referred to as cylinder heads A to F). The shape of the cylinder head is a substantially rectangular body in which a complicated hole is formed as shown in FIGS. 2 (a) and 2 (b).
For three of the six molded cylinder heads (referred to as cylinder heads A, B, and C), a closed space is formed with the valve seat on the cylinder-facing surface as a hardening target (see FIG. 3). A steel ball having a diameter of 15 mm and a steel ball having a diameter of 10 mm were put into the closed space as a hardening material, and were oscillated at a vibration frequency of 8 Hz and a shaking width of 60 mm to perform hardening treatment of the valve seat portion on the cylinder-facing surface. The swing direction was set to a direction substantially perpendicular to the cylinder head (direction indicated by arrow S in FIG. 3). The hardening treatment was not performed on the cylinder heads D, E and F among the six cylinder heads thus formed.
From the cylinder heads A to F, four test pieces including the valve seat 22 (see FIG. 2B) between the intake port 28 and the exhaust port 29 were cut out. Then, a tensile test and a hardness test were performed on each test piece as follows.
(Tensile test)
Tensile tests were performed using three of the test pieces obtained from the cylinder head A (Examples 1 to 3) and three of the test pieces obtained from the cylinder head D (Comparative Examples 1 to 3). The mechanical properties (tensile strength, 0.2% proof stress, elongation) were measured. FIG. 4 shows the results. In addition, the tensile test was performed based on Japanese Industrial Standards.
(Hardness Test 1)
Using four test pieces obtained from the cylinder head B (Examples 4 to 7) and four test pieces obtained from the cylinder head E (Comparative Examples 4 to 7), the surface of each test piece was A micro Vickers hardness test was performed on each of a portion having a depth of 40 μm and a portion having a depth of 2000 μm from the surface, and the hardness was measured. Table 2 shows the results. In addition, the micro Vickers hardness test was performed based on Japanese Industrial Standards.
[0070]
[Table 2]

(Hardness test 2)
The test piece used in Example 4 was subjected to a micro Vickers hardness test on a portion different from the hardness test 1 from the surface to a depth of 3 mm to measure the hardness. FIG. 6 shows the results. In addition, the hardness from the surface every 0.5 μm to every 50 μm, from every 0.5 mm to every 1.5 μm every 100 μm, and after every 1.5 mm deep every 200 μm. The test was performed.
(Hardness Test 3)
A Brinell hardness test was performed using three of the test pieces obtained from the cylinder head C (Examples 8 to 10) and three of the test pieces obtained from the cylinder head F (Comparative Examples 8 to 10). And hardness were measured. FIG. 5 shows the results. The Brinell hardness test was performed based on Japanese Industrial Standards.
[0075]
As described above, according to the present invention, a hardened casting in which a dense layer having a thickness of 300 to 2000 μm is formed on the surface side, or a Si content of 10% by mass or less. A non-heat-treated casting obtained by casting a casting aluminum alloy having a Cu content of 2% by mass or less, and having a 0.2% proof stress of 150 N / mm. ² As described above, a hardened casting having a hardness of 70 HB or more in Brinell hardness or 70 HV or more in micro Vickers hardness is provided. These hardened castings have narrow portions, and even when high pressure is applied thereto, problems such as cracks are unlikely to occur. Contributes to improving the reliability of diesel engines.
Further, according to the present invention, as a post-treatment for a casting, a method for hardening a casting for forming a dense layer having a constant thickness to improve hardness, and a method for manufacturing a casting including the hardening method are provided. Is done. Therefore, a casting with excellent hardness can be obtained by selecting a method with high productivity regardless of the casting method for obtaining the casting. Further, for example, even in the vicinity of a feeder portion at the time of casting of a casting, since excellent hardness can be imparted, the yield is not reduced by enlarging the feeder portion.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a method for producing a hardened casting according to the present invention, and FIGS. 1 (a), 1 (b) and 1 (c) are block flow diagrams of the production process.
FIG. 2 is a view showing a cylinder head for a diesel engine which is an example of a casting. FIG. 2 (a) is a cross-sectional view of a side surface when a cylinder facing surface is set downward, and FIG. FIG. 2A is a diagram viewed from below in FIG. 2A, and is a diagram illustrating a cylinder facing surface.
FIG. 3 is a cross-sectional view showing an embodiment of a casting hardening method according to the present invention, and is a diagram showing a closed space formed by an enclosure lid on a cylinder facing surface of a cylinder head which is an example of the casting.
FIG. 4 is a graph showing the results of a tensile test in Examples.
FIG. 5 is a graph showing the results of a Brinell hardness test in Examples.
FIG. 6 is a graph showing the results of a micro Vickers hardness test in Examples.
FIG. 7 is a perspective view showing one embodiment of a casting hardening device according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Casting process, 2 ... Hardening process, 3 ... Heat treatment process, 4 ... Flattening process, 20 ... Cylinder head, 21 ... Cylinder facing surface, 22 ... Valve seat, 23 ... Valve 28 ... Intake port, 29 ... Exhaust Port, 31: closed space, 32: enclosure lid, 33: room.

Claims (16)

A casting hardened by a dense layer formed on the surface side,
A hardened casting, wherein the dense layer has a thickness of 300 to 2000 μm. The hardened casting according to claim 1, which is cast using a material selected from the group consisting of AC2B, AC3A, AC4A, AC4CH, and AC4D, or a material in which two or more materials are mixed, as a main raw material. A non-heat-treated casting obtained by casting a casting aluminum alloy having a silicon content of 10% by mass or less and a copper content of 2% by mass or less,
A hardened casting having a 0.2% proof stress of 150 N / mm ² or more and a hardness of 70 HB or more in Brinell hardness or 70 HV or more in micro Vickers hardness. A cylinder head for a diesel engine, which is the hardened casting according to any one of claims 1 to 3. A method for producing a casting cured by a dense layer formed on the surface side,
After casting a casting by casting a molten metal into a mold to obtain a casting, at least one surface of the casting, to form a closed space with the one surface as a constituent surface, and put a hardening material into the closed space A method for producing a hardened casting, wherein the casting is oscillated to form a dense layer on the surface side of the casting including the one surface. The method for producing a hardened casting according to claim 5, further comprising a step of performing a heat treatment before or after forming the dense layer. The method for producing a hardened casting according to claim 5, further comprising a step of performing a flattening process on a surface of the casting including the one surface after forming the dense layer. A method of forming a dense layer on the surface side of the casting and curing the casting,
A method of hardening a casting, comprising forming a closed space having a surface of a casting as a constituent surface, and introducing a hardening material into the closed space to swing the casting. 9. The method for hardening a casting according to claim 8, wherein the frequency of the swing is approximately 5 to 20 Hz. The method for hardening a casting according to claim 8, wherein a swing width of the swing is approximately 30 to 200 mm. The method for curing a casting according to any one of claims 8 to 10, wherein a total swing time of the swing is approximately 3 to 120 minutes. The method for curing a casting according to any one of claims 8 to 11, wherein an amount of the hardening material charged is approximately 5 to 70% by volume with respect to the closed space. The method for hardening a casting according to any one of claims 8 to 12, wherein the hardening material is one or more of a mixture including at least a metal ball or a cut wire. The method for hardening a casting according to any one of claims 8 to 13, wherein a main material constituting the casting is cast iron or an aluminum alloy for casting. A device that forms a dense layer on the surface side of the casting and hardens the surface of the casting,
A pedestal that forms a closed space having the surface of the casting as a constituent surface and is capable of fixing the casting in which the hardening material is charged in the closed space in an arbitrary direction, and a swinging unit that swings the gantry. A casting hardening device. 16. The casting hardening device according to claim 15, wherein the swinging means has a motor and a crank connected to the motor.

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