Resulting Anodized Aluminum surface flooding after staining were the following main reasons:
1 piece caustic pre-treatment is not thorough enough.
(2) low melt temperature dyeing.
3 staining solution surface oil.
4 film did not retire net rework.
5 oxide film is contaminated.
6 After oxidation washed thoroughly enough, not cleaned.
7 aluminum anodizing current density is too large.
8 anodizing solution temperature is too low, the current density is too small.
9 aluminum anodizing solution temperature.
2013年10月23日星期三
2013年9月17日星期二
What effect anodized disposal
Aluminum and alloys after anodizing equipment disposal , you can make a layer made of aluminum and its alloys look much more than the natural oxide film thickness fine film . This layer of oxide film and then the whole story off manually dispose of non- crystalline oxide film into a crystalline oxide film , the pore is also closed , thus making the same metallic gloss appearance can be durable , corrosion function, the mechanical strength has increased , embellishment can be achieved by staining appearance . Because aluminum and its alloy products after anodizing the whole story has many features, so the Anodized Aluminum process in aluminum look wider use of disposal . Use in industry can be broadly divided into the following categories:
( 1) to avoid corrosion products : Because the anodized film obtained by the closure of the appropriate disposal of the whole story in the atmosphere has good stability . Whether from the sulfuric acid solution , oxalic acid or chromic acid solution obtained in the normal process of the oxide film , the corrosion is a very good function , such as household aluminum pan , pot, washing interior and so on. Chromic acid oxidation method for aluminum welding parts together and riveting pieces .
( 2 ) protection - embellishment : high transparency in the obtained oxide film , the oxide film can be adsorbed with a variety of organic dyes or inorganic pigments characteristics , the oxide film can be obtained in a variety of light colors and pictures handsome , and in recent years not the presentation of new technology , such as less oxidized repeated once colored fireworks picture , wood picture , oxidative handling offset printing , ceramic oxide , so that even more handsome aluminum pleasing appearance , this layer of film is both colorful decorative layer , but also resists , such as lighters , fountain pens and crafts.
( 1) to avoid corrosion products : Because the anodized film obtained by the closure of the appropriate disposal of the whole story in the atmosphere has good stability . Whether from the sulfuric acid solution , oxalic acid or chromic acid solution obtained in the normal process of the oxide film , the corrosion is a very good function , such as household aluminum pan , pot, washing interior and so on. Chromic acid oxidation method for aluminum welding parts together and riveting pieces .
( 2 ) protection - embellishment : high transparency in the obtained oxide film , the oxide film can be adsorbed with a variety of organic dyes or inorganic pigments characteristics , the oxide film can be obtained in a variety of light colors and pictures handsome , and in recent years not the presentation of new technology , such as less oxidized repeated once colored fireworks picture , wood picture , oxidative handling offset printing , ceramic oxide , so that even more handsome aluminum pleasing appearance , this layer of film is both colorful decorative layer , but also resists , such as lighters , fountain pens and crafts.
2013年9月12日星期四
Current Theories of aluminum stress corrosion
After more than a century of research , the mechanism for causing SCC academia there are still differences . Now generally accepted mechanism of hydrogen-induced cracking and anodic dissolution mechanism .
1 , hydrogen-induced cracking
Since the mid-seventies , many experiments show , 7 × × × series high strength aluminum alloy SCC is hydrogen-induced cracking mechanism . The theory is that : ( 1 ) the migration of hydrogen through the grain boundary dislocations to accumulate around the precipitates , the bonding strength of the grain boundaries greatly reduced , weakening the grain boundary , resulting in intergranular fracture ; ( 2 ) the accumulation of hydrogen within the crack , promote the formation of hydrogen pressure alloy fracture ; ( 3 ) to promote hydrogen alloy deformation which results in fracture ; ( 4 ) to promote the formation of hydride alloy fracture. currently proposed mechanism of hydrogen induced cracking has the following theory :
(a) hydrogen pressure of theory : When the metal present in supersaturated H, the microscopic defects in the various combined into H2, room temperature, the reaction is not reversible , that will not decompose into H2 H. H2 concentration increases as the defect , hydrogen pressure also increases when the hydrogen pressure is greater than the yield strength will produce local plastic deformation , so that the surface muster , forming hydrogen bubbles .
(b) a weak bond theory : reduction of hydrogen atoms in the metal bond strength , when the local stress concentration equal atomic bonding force of atomic bond rupture, micro- crack nucleation .
(c) reduce the surface energy of hydrogen theory : hydrogen bonding force at the same time reduce the inevitable lowering the surface energy , and vice versa . hydrogen adsorbed on the metal surface inside the crack , the surface can be reduced , resulting in crack instability critical stress required to decline due to did not consider the plastic deformation work , so the metal does not apply.
(d) Comprehensive hydrogen induced cracking mechanism : This mechanism considering promoting local plastic deformation of hydrogen , hydrogen atoms bond together and reduce the role of hydrogen pressure .
2 , anodic dissolution
Anodic dissolution theory [ 7-9 ] that the anodic dissolution of the metal continues to lead SCC crack nucleation and expansion , resulting in the fracture alloy Anodized Aluminum dissolution SCC main points of the theory are as follows:
( 1 ) Anode channel Theory : the corrosion along the local channels and cracks occur , the tensile stress perpendicular to the channel , the local concentration of stress on the crack tip . Aluminum alloy anode channel consists of a pre-existing grain boundary phase difference caused by the substrate potential , and then the crack opening stress exposing a fresh surface in this case , accelerated corrosion along the grain boundaries .
( 2 ) slip dissolution theory: the occurrence of SCC aluminum oxide film on the surface of the existence of local weak spots in the alloy matrix under stress along the sliding parts arising wrong move , the formation of slip ladder when sliding ladder , surface film can not slip ladder with the formation of the corresponding deformation occurs , the membrane will rupture and fresh bare surface in contact with the corrosive medium , undergoing rapid anodic dissolution .
( 3 ) membrane rupture theory: the presence of corrosive media, metal surface protection film , as reactive ion suffer from stress or rupture caused by the action of , exposed fresh surface with the rest of the surface film to form the small yang great cathode corrosion cell , resulting in fresh surface of the anode dissolved.
3 , anodic dissolution and hydrogen-induced cracking joint action
Anodic dissolution and hydrogen-induced cracking are two different concepts, simple anodic dissolution can be prevented by cathodic protection , and for the hydrogen-induced cracking, cathodic polarization tend to promote cracking and some system dominated by anodic dissolution , some places hydrogen mainly induced cracking of aluminum alloys SCC often include both process and to a sharp distinction between the two phenomena is actually difficult.
Najjar , etc. [ 10 ] found that 7050 aluminum alloy in 3% NaCl solution SCC is due to anodic dissolution and hydrogen-induced cracking result of joint action . Initially, the alloy grain boundaries particle potential difference exists , the occurrence of local anodic dissolution , resulting in rupture of the passive film formed critical defects , micro- crack initiation with partial anodic dissolution of grain boundary increases, reducing the H atoms diffuse into the process zone , and microscopic characteristics of the structure , the crack tip stress and plastic strain interactions , causing damage .
In addition to the SCC mechanism , the researchers also studied the SCC from other angles mechanisms , including SCC surface migration theory , SCC dislocation -free zone theory and semi-empirical model of crack growth .
1 , hydrogen-induced cracking
Since the mid-seventies , many experiments show , 7 × × × series high strength aluminum alloy SCC is hydrogen-induced cracking mechanism . The theory is that : ( 1 ) the migration of hydrogen through the grain boundary dislocations to accumulate around the precipitates , the bonding strength of the grain boundaries greatly reduced , weakening the grain boundary , resulting in intergranular fracture ; ( 2 ) the accumulation of hydrogen within the crack , promote the formation of hydrogen pressure alloy fracture ; ( 3 ) to promote hydrogen alloy deformation which results in fracture ; ( 4 ) to promote the formation of hydride alloy fracture. currently proposed mechanism of hydrogen induced cracking has the following theory :
(a) hydrogen pressure of theory : When the metal present in supersaturated H, the microscopic defects in the various combined into H2, room temperature, the reaction is not reversible , that will not decompose into H2 H. H2 concentration increases as the defect , hydrogen pressure also increases when the hydrogen pressure is greater than the yield strength will produce local plastic deformation , so that the surface muster , forming hydrogen bubbles .
(b) a weak bond theory : reduction of hydrogen atoms in the metal bond strength , when the local stress concentration equal atomic bonding force of atomic bond rupture, micro- crack nucleation .
(c) reduce the surface energy of hydrogen theory : hydrogen bonding force at the same time reduce the inevitable lowering the surface energy , and vice versa . hydrogen adsorbed on the metal surface inside the crack , the surface can be reduced , resulting in crack instability critical stress required to decline due to did not consider the plastic deformation work , so the metal does not apply.
(d) Comprehensive hydrogen induced cracking mechanism : This mechanism considering promoting local plastic deformation of hydrogen , hydrogen atoms bond together and reduce the role of hydrogen pressure .
2 , anodic dissolution
Anodic dissolution theory [ 7-9 ] that the anodic dissolution of the metal continues to lead SCC crack nucleation and expansion , resulting in the fracture alloy Anodized Aluminum dissolution SCC main points of the theory are as follows:
( 1 ) Anode channel Theory : the corrosion along the local channels and cracks occur , the tensile stress perpendicular to the channel , the local concentration of stress on the crack tip . Aluminum alloy anode channel consists of a pre-existing grain boundary phase difference caused by the substrate potential , and then the crack opening stress exposing a fresh surface in this case , accelerated corrosion along the grain boundaries .
( 2 ) slip dissolution theory: the occurrence of SCC aluminum oxide film on the surface of the existence of local weak spots in the alloy matrix under stress along the sliding parts arising wrong move , the formation of slip ladder when sliding ladder , surface film can not slip ladder with the formation of the corresponding deformation occurs , the membrane will rupture and fresh bare surface in contact with the corrosive medium , undergoing rapid anodic dissolution .
( 3 ) membrane rupture theory: the presence of corrosive media, metal surface protection film , as reactive ion suffer from stress or rupture caused by the action of , exposed fresh surface with the rest of the surface film to form the small yang great cathode corrosion cell , resulting in fresh surface of the anode dissolved.
3 , anodic dissolution and hydrogen-induced cracking joint action
Anodic dissolution and hydrogen-induced cracking are two different concepts, simple anodic dissolution can be prevented by cathodic protection , and for the hydrogen-induced cracking, cathodic polarization tend to promote cracking and some system dominated by anodic dissolution , some places hydrogen mainly induced cracking of aluminum alloys SCC often include both process and to a sharp distinction between the two phenomena is actually difficult.
Najjar , etc. [ 10 ] found that 7050 aluminum alloy in 3% NaCl solution SCC is due to anodic dissolution and hydrogen-induced cracking result of joint action . Initially, the alloy grain boundaries particle potential difference exists , the occurrence of local anodic dissolution , resulting in rupture of the passive film formed critical defects , micro- crack initiation with partial anodic dissolution of grain boundary increases, reducing the H atoms diffuse into the process zone , and microscopic characteristics of the structure , the crack tip stress and plastic strain interactions , causing damage .
In addition to the SCC mechanism , the researchers also studied the SCC from other angles mechanisms , including SCC surface migration theory , SCC dislocation -free zone theory and semi-empirical model of crack growth .
2013年9月6日星期五
Aluminum and aluminum alloy anodized role
Aluminum and its alloys it will be oxidized in air is known , the aluminum surface is naturally formed oxide film of non- crystalline , it will make the surface of the aluminum metal lose their luster , though this layer of the natural oxide film causes the aluminum metal surface slightly passivated , but very thin , about 4 ~ 5nm, and the porosity , the mechanical properties are poor, it can not effectively prevent the air of various media further corrosion of the aluminum metal .
After anodic oxidation treatment , the aluminum and its alloys can be obtained on the surface layer is much more than the natural oxide film thickness of the dense layer ( from tens to hundreds of micrometers or microns). This layer and then through the artificial oxide film sealing treatment , non- crystalline form of the oxide film into a crystalline oxide film , pores can be closed, so the surface luster of the metal over the long term , corrosion resistance , mechanical strength are improved , dyed also receive decorative appearance. Since aluminum and its alloy products after anodizing has many features , so aluminum anodizing surface treatment of aluminum products in a wider application . In industrial applications can be divided into the following categories .
( 1) to prevent corrosion products : the anodic oxidation film obtained after proper sealing treatment in the atmosphere has good stability . Whether from the sulfuric acid solution , oxalic acid or chromic acid solution obtained in the normal process of the oxide film , which is a very good corrosion resistance , such as household aluminum pan , pot, washing interior and so on. Chromic acid oxidation method is particularly suitable for aluminum welding parts and riveting pieces .
( 2 ) protection - decoration : high transparency in the obtained oxide film , the oxide film can be adsorbed with a variety of organic dyes or inorganic pigments characteristics , the oxide film obtained bright light of various colors and patterns , and in recent years not the emergence of new technology , such as less oxidation times a colored fireworks pattern , wood grain pattern , oxidation offset transfer printing , ceramic oxide , so that the aluminum look more beautiful looking, this layer of color film is both a decorative layer , but also resists , such as lighters , fountain pens and crafts.
( 3 ) as the hard wear layer : in sulfuric acid or oxalic acid solution can be adjusted by the anodization process conditions , to obtain thick and hard layer , the use of film holes and to store the selective absorption properties of the fuel , used effectively to work under conditions of friction state , both lubrication and wear characteristics , such as cars and tractors engine cylinder , piston .
( 4 ) as an electrical insulating layer : Anodized Aluminum and its alloys oxide film having a large resistance characteristics, and the resistance is proportional to the thickness of the film , this feature as an electrical insulating property has a certain practical significance , can be used as capacitors the dielectric can also be used for alumina leather outer cable sheath , its surface layer for insulation instead of rubber and plastic foreskin foreskin is more popular in foreign countries , when the thickness of 27.5μm , the breakdown voltage of 441V. The use of phenolic resin as pore filling , which can increase wear voltage 2 times in the oxalic acid solution , when the film thickness increases , the availability of resistance 200Ω, the breakdown voltage of 980V for quality insulating layer , of course, to use this feature except for the conductor , but also can be used for other electrical appliances and so on.
( 5 ) for painting , plating the bottom : the oxide layer having a porous adsorption capacity and good , and the film and the organic film with good adhesion , the underlying paint can be used . Of phosphoric acid anodized aluminum plating film can be used as the bottom .
( 6 ) used in modern architecture : Since the introduction of aluminum electrolytic coloring process , in recent years, the domestic aspects of architectural aluminum electrolytic coloring applied to the increasing , it is not only suitable for architectural bronze shades , black, red , with its excellent abrasion resistance conventional oxidation in general , particularly worth mentioning is very good fastness , more than 20 years in the atmosphere Needless sun dew color , which is incomparable with oxidative coloring . Oxidized aluminum electrolytic coloring method can be used in building windows and doors not only to do with it shop counters , shelves, etc. are also particularly suitable.
After anodic oxidation treatment , the aluminum and its alloys can be obtained on the surface layer is much more than the natural oxide film thickness of the dense layer ( from tens to hundreds of micrometers or microns). This layer and then through the artificial oxide film sealing treatment , non- crystalline form of the oxide film into a crystalline oxide film , pores can be closed, so the surface luster of the metal over the long term , corrosion resistance , mechanical strength are improved , dyed also receive decorative appearance. Since aluminum and its alloy products after anodizing has many features , so aluminum anodizing surface treatment of aluminum products in a wider application . In industrial applications can be divided into the following categories .
( 1) to prevent corrosion products : the anodic oxidation film obtained after proper sealing treatment in the atmosphere has good stability . Whether from the sulfuric acid solution , oxalic acid or chromic acid solution obtained in the normal process of the oxide film , which is a very good corrosion resistance , such as household aluminum pan , pot, washing interior and so on. Chromic acid oxidation method is particularly suitable for aluminum welding parts and riveting pieces .
( 2 ) protection - decoration : high transparency in the obtained oxide film , the oxide film can be adsorbed with a variety of organic dyes or inorganic pigments characteristics , the oxide film obtained bright light of various colors and patterns , and in recent years not the emergence of new technology , such as less oxidation times a colored fireworks pattern , wood grain pattern , oxidation offset transfer printing , ceramic oxide , so that the aluminum look more beautiful looking, this layer of color film is both a decorative layer , but also resists , such as lighters , fountain pens and crafts.
( 3 ) as the hard wear layer : in sulfuric acid or oxalic acid solution can be adjusted by the anodization process conditions , to obtain thick and hard layer , the use of film holes and to store the selective absorption properties of the fuel , used effectively to work under conditions of friction state , both lubrication and wear characteristics , such as cars and tractors engine cylinder , piston .
( 4 ) as an electrical insulating layer : Anodized Aluminum and its alloys oxide film having a large resistance characteristics, and the resistance is proportional to the thickness of the film , this feature as an electrical insulating property has a certain practical significance , can be used as capacitors the dielectric can also be used for alumina leather outer cable sheath , its surface layer for insulation instead of rubber and plastic foreskin foreskin is more popular in foreign countries , when the thickness of 27.5μm , the breakdown voltage of 441V. The use of phenolic resin as pore filling , which can increase wear voltage 2 times in the oxalic acid solution , when the film thickness increases , the availability of resistance 200Ω, the breakdown voltage of 980V for quality insulating layer , of course, to use this feature except for the conductor , but also can be used for other electrical appliances and so on.
( 5 ) for painting , plating the bottom : the oxide layer having a porous adsorption capacity and good , and the film and the organic film with good adhesion , the underlying paint can be used . Of phosphoric acid anodized aluminum plating film can be used as the bottom .
( 6 ) used in modern architecture : Since the introduction of aluminum electrolytic coloring process , in recent years, the domestic aspects of architectural aluminum electrolytic coloring applied to the increasing , it is not only suitable for architectural bronze shades , black, red , with its excellent abrasion resistance conventional oxidation in general , particularly worth mentioning is very good fastness , more than 20 years in the atmosphere Needless sun dew color , which is incomparable with oxidative coloring . Oxidized aluminum electrolytic coloring method can be used in building windows and doors not only to do with it shop counters , shelves, etc. are also particularly suitable.
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